fixed  #435, fix #423  #426,  #430 (suggestions: 2,3): added build flag option to .condarc

 * add ability to configure build flags within .condarc: LINUX/Mac OSX
    CPPFLAGS, CFLAGS, CXXFLAGS, LDFLAGS, FFLAGS, FFLAGS, MAKEOPTS, CHOST,
    MACOSX_DEPLOYMENT_TARGET: see issue #435, fix #423
  * fixed minor issues: #426,  #430 (suggestions: 2,3)

NOTE: MACOSX where not checked at all (no MAC)
see:comment #FIX ME:  in environ.py : maybe they should be also
only be exported when set: similar to Linux
FORTRAN Flags export where also not checked

P