pgsql: Back-patch fix for extraction of fixed prefixes from regular exp

Back-patch fix for extraction of fixed prefixes from regular expressions.

Back-patch of commits 628cbb50ba80c83917b07a7609ddec12cda172d0 and
c6aae3042be5249e672b731ebeb21875b5343010. This has been broken since
7.3, so back-patch to all supported branches.

Branch
------
REL9_2_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/18c8dc32ce6759a8837f01e3dd0036cd19ee8683

Modified Files
--------------
src/backend/regex/Makefile | 2 +-
src/backend/regex/README | 4 +-
src/backend/regex/regc_color.c | 11 ++-
src/backend/regex/regc_nfa.c | 34 +++---
src/backend/regex/regcomp.c | 2 +-
src/backend/regex/rege_dfa.c | 11 +-
src/backend/regex/regprefix.c | 259 +++++++++++++++++++++++++++++++++++
src/backend/utils/adt/regexp.c | 65 +++++++++
src/backend/utils/adt/selfuncs.c | 209 +++++-----------------------
src/include/regex/regex.h | 4 +
src/include/regex/regguts.h | 39 ++++--
src/include/utils/builtins.h | 2 +
src/test/regress/expected/regex.out | 63 +++++++++
src/test/regress/sql/regex.sql | 10 ++
14 files changed, 505 insertions(+), 210 deletions(-)