Use PCRE posix-compatability library for regex handling

We let users generate sieve scripts with regular expressions
in them, and occasionally these combine in ugly ways with
incoming messages (i.e. a message with hundreds of recipients
and an inefficient regex match on recipient addresses caused
an lmtp process to grow to over 2Gb in size before it died)

This patch tests for the presence of the PCRE library and
uses it by preference if available.  NOTE: you will need
to run autoconf again on your source tree after applying 
this patch, because it changes configure.in.

Index: cyrus-imapd-2.3.9/configure.in
===================================================================
--- cyrus-imapd-2.3.9.orig/configure.in	2006-12-01 04:11:16.000000000 +1100
+++ cyrus-imapd-2.3.9/configure.in	2007-09-11 17:16:54.000000000 +1000
@@ -243,10 +243,13 @@
 	AC_PROG_LEX
 	AC_CHECK_LIB(fl,main)
 
+ 	AC_SEARCH_LIBS(regcomp, pcreposix, [LIBS="${LIBS} -lpcre -lpcreposix"
+ 			AC_DEFINE(ENABLE_REGEX,[],[Do we have a decent regex library?])
+		 	AC_CHECK_HEADER(pcreposix.h, AC_DEFINE(HAVE_PCREPOSIX,[],[Do we have pcreposix.h?]))])
+
  	AC_SEARCH_LIBS(regcomp, rx regex, [
  			AC_DEFINE(ENABLE_REGEX,[],[Do we have a decent regex library?])
 		 	AC_CHECK_HEADER(rxposix.h, AC_DEFINE(HAVE_RX,[],[Do we have rxposix.h?]))])
-  		
 
 	SIEVE_SUBDIRS="${SIEVE_SUBDIRS} $sievedir"
 	EXTRA_OUTPUT="${EXTRA_OUTPUT} $sievedir/Makefile"
Index: cyrus-imapd-2.3.9/sieve/comparator.h
===================================================================
--- cyrus-imapd-2.3.9.orig/sieve/comparator.h	2006-12-01 04:11:24.000000000 +1100
+++ cyrus-imapd-2.3.9/sieve/comparator.h	2007-09-11 17:04:34.000000000 +1000
@@ -29,6 +29,9 @@
 #define COMPARATOR_H
 
 #ifdef ENABLE_REGEX
+#ifdef HAVE_PCREPOSIX
+#include <pcreposix.h>
+#else
 #ifdef HAVE_RX
 #include <rxposix.h>
 #else
@@ -36,6 +39,7 @@
 #include <regex.h>
 #endif
 #endif
+#endif
 
 /* compares pat to text; returns 1 if it's true, 0 otherwise 
    first arg is text, second arg is pat, third arg is rock */