Check for pcre.h in configure.ac
Add support for older versions of flex (tiny change)

E.g. flex 2.5.4 (Solaris 10) does not like a space after -o.
src/iri.c: Use c_strcasestr instead of strcasestr

This also fixes a problem with strcasestr not being in the
boostrap.conf module list.

Reported-by: Kiyoshi KANAZAWA <yoi_no_myoujou@yahoo.co.jp>
bootstrap.conf: Add module 'getline'

This function does not exist in some older C libraries.
src/iri.c: Call xstrndup instead of strndup

strndup() does not exist in some older C libraries, also xstrndup()
exits on memory allocation failures.