t/lib-http.sh: Restructure finding of default httpd location

t/lib-http.sh: Restructure finding of default httpd location

On CentOS 5, httpd is located at /usr/sbin/httpd, and the modules are
located at /usr/lib64/httpd/modules.  To enable easy testing of httpd,
we would like those locations to be detected automatically.

uname might not be the best way to determine the default location for
httpd since different Linux distributions apparently put httpd in
different places, so we test a couple different locations for httpd,
and use the first one that we come across.  We do the same for the
modules directory.

cc: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Tarmigan Casebolt <tarmigan+git@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>