Remove stray dead code
Take into account that misc/install-gnu-gcc-osx has changed names
Fix recently introduced bug in string->number (a bignum addition was mistakenly replaced by a fixnum addition)
Use consistent naming for specialized versions of number->string
Add definitions of C math library functions that may be missing (high accuracy implementation is still TODO)
Use GNU gcc to build prebuilt Gambit for OS X
Improve level of debugging messages when building prebuilt Gambit installers