doc: Change email address to maan@tuebingen.mpg.de

The mail server on systemlinux.org was down for more than a week
lately, so let's use an alternative official address.  This commit
changes all maan@systemlinux.org addresses to maan@tuebingen.mpg.de.

Most .c and .h files contain the email address in the copyright header,
so they must all be patched. Three other files contain the address
for a different reason:

	* README lists email and git, gitweb and home page URLs
	* configure.ac needs it for configure -h
	* version.c contains it for the -V option of all commands