When reading PO files, treat CRLF line terminators like LF.

When reading PO files, treat CRLF line terminators like LF.

Reported by Hendy Irawan <hendy@hendyirawan.com> at
<https://savannah.gnu.org/bugs/?52395>.

* gettext-tools/src/read-po-internal.h (MBFILE_MAX_PUSHBACK): Renamed from
NPUSHBACK. Increase by 1.
(struct mbfile): Rename field 'have_pushback' to 'pushback_count'.
* gettext-tools/src/read-po-lex.c (mbfile_init): Update.
(mbfile_getc): Read pushed-back character before testing for sticky EOF.
(mbfile_ungetc): Update.
(mbfile_getc_normalized): New function.
(lex_getc): Invoke mbfile_getc_normalized instead of mbfile_getc.
* gettext-tools/tests/testdata/crlf.pot: New file.
* gettext-tools/tests/msgcat-23: New file.
* gettext-tools/tests/Makefile.am (TESTS): Add it.