- Add an ECL option to build maxima using ecl lisp. Option enabled by default so that Sage can work properly when using packages. 
- Add a SAGE option (implies ECL) to apply some patches so that Sage can work properly. This option is also enabled by default to get working Sage packages. 
- Fix a bug in xmaxima about documentation. This also introduces an XMAXIMA option (enabled by default) because to have xmaxima working we need to ensure that DOCS and TEST are enabled, which is done by using XMAXIMA_IMPLIES. This also has the advantage to remove USES= tk for users who want to disable XMAXIMA. 
 Based on an original submission by thierry.
 Reported by: thierry