[perl #132665] Always use STOP_AT_PARTIAL in PerlIO::encoding

# New Ticket Created by  Leon Timmermans 
# Please include the string:  [perl #132665]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=132665 >


This is a bug report for perl from fawaka@gmail.com,
generated with the help of perlbug 1.40 running under perl 5.24.0.


-----------------------------------------------------------------
[Please describe your issue here]

PerlIO::encoding has a $fallback variable that allows one to set the
behavior on a encoding/decoding error, for example to make it throw an
exception on error. What is not documented (actually the example in the
documentation is even missing this) is that PerlIO::encoding needs the
(equally undocumented) Encode::STOP_AT_PARTIAL flag to be set, otherwise
a multi-byte character spanning buffer boundaries will be interpreted as
two invalid byte sequences. I could have fixed the documentation, but
instead I fixed the code to always pass this flag to Encode, simplifying
the use and making the current documentation correct again.

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=library
    severity=low
    module=PerlIO::encoding
---
Site configuration information for perl 5.24.0:

Configured by leont at Thu Jun  9 10:14:26 CEST 2016.

Summary of my perl5 (revision 5 version 24 subversion 0) configuration:

  Platform:
    osname=linux, osvers=4.5.4-1-arch, archname=x86_64-linux-thread-multi
    uname='linux leon-laptop 4.5.4-1-arch #1 smp preempt wed may 11
22:21:28 cest 2016 x86_64 gnulinux '
    config_args='-de
-Dprefix=/home/leont/perl5/perlbrew/perls/perl-5.24.0 -Dusethreads
-Aeval:scriptdir=/home/leont/perl5/perlbrew/perls/perl-5.24.0/bin'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv
-fno-strict-aliasing -pipe -fstack-protector-strong
-I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing
-pipe -fstack-protector-strong -I/usr/local/include'
    ccversion='', gccversion='6.1.1 20160501', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8,
byteorder=12345678, doublekind=3
    d_longlong=define, longlongsize=8, d_longdbl=define,
longdblsize=16, longdblkind=3
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t',
lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib
/usr/lib/gcc/x86_64-pc-linux-gnu/6.1.1/include-fixed /usr/lib
/lib/../lib /usr/lib/../lib /lib /lib64 /usr/lib64
    libs=-lpthread -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.23.so, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version='2.23'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -L/usr/local/lib
-fstack-protector-strong'

Locally applied patches:
    Devel::PatchPerl 1.40

---
@INC for perl 5.24.0:
    /home/leont/perl5/perlbrew/perls/perl-5.24.0/lib/site_perl/5.24.0/x86_64-linux-thread-multi
    /home/leont/perl5/perlbrew/perls/perl-5.24.0/lib/site_perl/5.24.0
    /home/leont/perl5/perlbrew/perls/perl-5.24.0/lib/5.24.0/x86_64-linux-thread-multi
    /home/leont/perl5/perlbrew/perls/perl-5.24.0/lib/5.24.0
    .

---
Environment for perl 5.24.0:
    HOME=/home/leont
    LANG=en_US.UTF-8
    LANGUAGE=en_US.UTF-8
    LC_MEASUREMENT=en_IE.UTF-8
    LC_MESSAGES=POSIX
    LC_MONETARY=en_IE.UTF-8
    LC_PAPER=en_IE.UTF-8
    LC_TIME=en_IE.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/leont/perl5/perlbrew/bin:/home/leont/perl5/perlbrew/perls/perl-5.24.0/bin:/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl
    PERLBREW_HOME=/home/leont/.perlbrew
    PERLBREW_MANPATH=/home/leont/perl5/perlbrew/perls/perl-5.24.0/man
    PERLBREW_PATH=/home/leont/perl5/perlbrew/bin:/home/leont/perl5/perlbrew/perls/perl-5.24.0/bin
    PERLBREW_PERL=perl-5.24.0
    PERLBREW_ROOT=/home/leont/perl5/perlbrew
    PERLBREW_SHELLRC_VERSION=0.82
    PERLBREW_VERSION=0.82
    PERL_BADLANG (unset)
    SHELL=/bin/bash

• [perl #132665] Always use STOP_AT_PARTIAL in PerlIO::encoding by Leon Timmermans