(re_compile_pattern, re_comp, regerror): Add gettext wrapper.

(re_compile_pattern, re_comp, regerror): Add gettext wrapper.
(re_error_msgid): Renamed from `re_error_msg', for consistency
with other source files that declare arrays of message ids.
Identifiers ending in `msgid' are special to to some prototype
message-extracting utilities.
Make "Success" be the 0th entry, so it can be extracted too.
(re_comp): Replace "Memory exhausted" with
re_error_msgid[REG_ESPACE], to aid message consistency.