pcre.h failure in grep-2.5.4-20090126

[Karl Berry]

In grep-2.5.4-20090126, search.c says:

#ifdef HAVE_LIBPCRE
# include <pcre.h>
#endif

Unfortunately this does not work on my system, which is the oldish
Red Hat WS 4 (but compiling with the newish gcc 4.2.4).  On that system,
it's <pcre/pcre.h>.  When I change the #include, everything compiles
(with some mbs warnings), and all tests pass.

It would suffice to add a check for <pcre.h> and simply disable pcre if
it doesn't exist -- no real need to cater for this old system (although
if you want to check for <pcre/pcre.h>, fine too).  Hmm, there used to
be a configure option for it, but I see it's been "improved" to use
pcre-config and there is no manual override, so I don't know what to do.

karl