Added a constat to all files in functions/ to be able to chech whether the

Added a constat to all files in functions/ to be able to chech whether the
file has already been included.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@255 7612ce4b-ef26-0410-bec9-ea0150e637f0