* extconf.rb, exec_make.rb: Support MSVC++(nmake).
* libglade/extconf.rb: Fix compiling error on MSVC+.
* README, NEWS: Revised.
* extconf.rb, exec_make.rb: Add --strict option.
If you don't give this option, it doesn't exit with 1
(exit(1)) because it doesn't mean failure of compilation
and instalation of almost of all libraries.
* exec_make.rb: exit with 1 when failure occurred.
* exec_make.rb: don't use parenthesis in the argument of system()
for mingw32 support.