pcre.c: Version 8.20 added pcre_free_study(). Make use of this to free edata.
pcre.c: Use autoconf to detect if pcre_free_study() is available.
pcre.c: Use HAFE_PCRE_FREE_STUDY to guard other uses of pcre_free_study().
txlog: Add some more default headers to record in the txlog.
header_order: Add I=Connection mapping to default request header mapping.
docs: Document header_order module directives and vars.