Limit stack usage of libPCRE (and raise an exception when it runs out of stack space, for diagnosibility).

Also, do not accept some super old (>4 year old) pcre versions; as they can severely cripple regexp support, and intefere with this bugfix. Also tweak the message about missing PCRE in configure check --- libPCRE doesn't result in "better" regexp support; the support w/o it is a last-resort fallback...

Based on patch by Sune Vuorela (username debian, hostname pusling, tld com)