doc: reword "config file" to "configuration file"
While we do use the abbreviation "config" elsewhere in the docs, the
phrase "configuration file" is always written out in full, except in
this location in phases.txt.
--- a/mercurial/help/phases.txt Wed Jun 05 21:16:49 2013 +0200
+++ b/mercurial/help/phases.txt Thu Jun 06 13:37:41 2013 -0400
@@ -52,7 +52,7 @@
[phases]
publish = False
-See :hg:`help config` for more information on config files.
+See :hg:`help config` for more information on configuration files.
.. note::
Servers running older versions of Mercurial are treated as