Misc cleanups.
Handle 'has' for signatures in interpreter.
Allow calling type-valued functions in Spad.
Change '**' to '^' in src/input/*.
Avoid infinite recursion when evaluationg 'Record'.
Declare '$inRetract'.
Avoid infinite recursion during convertion.
Add missing definitions of '^'.
Eliminate use of SubsetCategory.
Add matrix versions of linear dependence routines.