Added a script for automatically bumping bjam version.

* jam_src/bump_version.py
  The script

* jam_src/jam.c
  Change version specification so that it's easier to change it by regexp.


[SVN r21196]

tools/build

@@ -1 +1 @@
-Subproject commit 7a92f8cbcbbebf5dacc9e419aecea7584afc0db3
+Subproject commit f78c05c27b3d069431538d83ce00df2b831edc96