Fix the following problems with version 1.31 of the xbanner port.
- installing in libexec directory isn't useful
- app-defaults file could only be found when XAPPLRESDIR enviroment variable is set -> patch in sourcefile is needed
- some compiler warnings and gets usage is fixed
- wrong usage of isnumber macro fixed
PR: 11768
Submitted by: Lars Koeller <lkoeller@cc.fh-lippe.de>