Update required wxWidgets to at least 2.9.5.
Update friend declarations to conform to modern standards regarding default arguments.
Workaround for compile error in wxWidgets

The wxWidgets macro wxFinite calls isfinite; on recent C++ compilers
this raises an error, as the more proper call is std::isfinite.
This commit manually redefines this macro in the source files where
it is called; a less than elegant but probably essential solution.
Correct infinite loop when parsing savefile with unbalanced quotes.

A savefile which had unbalanced quotes in the last quotes field would
result in the parser entering an infinite loop.  This is now fixed.

Fixes issue #118.
Merge branch 'maint13'

Merge maintenance branch of Gambit 13 into Gambit 14; add
descriptive error message on savefile parsing with unbalanced quotes.