msgconv: Handle protected file names with spaces.

msgconv: Handle protected file names with spaces.

* gettext-tools/src/po-charset.h (po_lex_isolate_start, po_lex_isolate_end): New
declarations.
* gettext-tools/src/po-charset.c (po_lex_isolate_start, po_lex_isolate_end): New
variables.
(po_lex_charset_init, po_lex_charset_set, po_lex_charset_close): Initialize
them.
* gettext-tools/woe32dll/gettextsrc-exports.c: Export also po_lex_isolate_start,
po_lex_isolate_end.
* gettext-tools/src/read-catalog-abstract.c: Include <stdbool.h>, po-charset.h.
(po_parse_comment_filepos): Parse the syntax of file names surrounded by control
characters.
* gettext-tools/src/msgl-iconv.c: Include msgl-ofn.h.
(iconv_msgdomain_list): Signal error if the target encoding does not contain the
control characters needed for escaping file names with spaces.
* gettext-tools/tests/msgconv-8: New file.
* gettext-tools/tests/Makefile.am (TESTS): Add it.