Partially revert r1203861: use a fixed string

Partially revert r1203861: use a fixed string
per module as the proxy_function instead of
the macro __FUNCTION__ which is not C89.

There's no real loss of information, because all
of the calls are in the same scgi handler function.

All proxy modules apart form SCGI already use the
upper case scheme in the analogous calls.

Backport of r1210124 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1210125 13f79535-47bb-0310-9956-ffa450edef68