[svn-r27645] Updates to older special config files in configure.ac:

- solaris2.x renamed to solaris. There are recent changes to this file
  but the "2.x" is misleading since the changes are applied to all
  versions.

- Removed support for OSF 4.x/5.x (Digital and Tru64 Unix). We no
  longer have the config files for these.

Tested on: jam (autogen.sh only)
           emu (Solaris 11)

configure.ac

@@ -247,14 +247,8 @@ case $host_os in
   freebsd*)
     host_os_novers=freebsd
     ;;
-  osf4.*)
-    host_os_novers=osf4.x
-    ;;
-  osf5.*)
-    host_os_novers=osf5.x
-    ;;
-  solaris2.*)
-    host_os_novers=solaris2.x
+  solaris*)
+    host_os_novers=solaris
     ;;
   *)
     host_os_novers=$host_os