Add tribits_tag_prefix.txt for targeted version info

This now puts a targeted tag prefix for TriBITS documentation.  Now it shows
'tribits-start-<num-commits>-<sha1>' instead of tags for VERA releases.  When
I do a TriBITS release, this will get updated appropriately to show the
release version number.

Author: Roscoe A. Bartlett

tribits/doc/utils/gen_doc_utils.sh

@@ -45,13 +45,15 @@ function update_if_different {
 
 function generate_git_version_file {
 
+  _TRIBITS_TAG_PREFIX=`cat ../../../tribits_tag_prefix.txt`
+
   if [ -e ../../../.git ] ; then
     echo
     echo "Generating git version"
     echo
-    echo `git describe` > TribitsGitVersion.txt
+    echo `git describe --match="$_TRIBITS_TAG_PREFIX*"` > TribitsGitVersion.txt
   else
-    echo "Unknown version" > TribitsGitVersion.txt
+    echo "$_TRIBITS_TAG_PREFIX.{Unknown version}" > TribitsGitVersion.txt
   fi
 
 }

tribits_tag_prefix.txt

@@ -0,0 +1 @@
+tribits_start