Extend mod_setenvif to support specifying regular expressions

on the SetEnvIf (and SetEnvIfNoCase) directive attribute field.
Example:  SetEnvIf ^TS*  [a-z].* HAVE_TS
will cause HAVE_TS to be set if any of the request headers begins
with "TS" and has a value that begins with any character in the
set [a-z]. [Bill Stoddard]


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@89353 13f79535-47bb-0310-9956-ffa450edef68