scheme: avoid call to un-needed functions

Neither the mark, nor the uuid free, are needed. So
don't call these functions; this will save some cpu time.
Hack around memory leak.

Someone needs to fix the python bindings so that they actually
work correctly.
Change to signals function signature
Remove stale boost header file
Fix third and final mem leak.

AtomTable atom-set was not being properly maintained.
Merge pull request #512 from linas/learn

Learn