fix build: add LIBS flag. and fix quoted arguments on windows.
"#{MRUBY_ROOT}/mrbgems/g" add to the default search path
minirake exit status not 0, when build failed.
Merge pull request #641 from iij/pr-minirake-exit-status

minirake exit status not 0, when build failed.
Merge pull request #640 from iij/pr-mrbgems-support-relative-path

GEMS.active support relative path
Merge pull request #639 from mattn/fix_build

fix build
Rakefile: LIBS default to -lm
add AR, YACC flags.
refactoring src/dump.c
Merge pull request #642 from iij/pr-fix-build-make-flags

add AR, YACC flags.
Merge pull request #643 from iij/pr-refactoring-dump

refactoring src/dump.c
Derive DISABLE_GEMS macro according to build configuration
Merge pull request #644 from xxuejie/derive-disable-gems

Derive DISABLE_GEMS macro according to build configuration
fix memory leak in fuction:make_cdump_irep
Merge pull request #645 from skandhas/pr-fix-memory-leak-in-make_cdump_irep

fix memory leak in function: make_cdump_irep
MSVC: include float header for _isnan and _finite
Update Array#each to be slightly faster.
Merge pull request #646 from cremno/msvc-include-float-header

MSVC: include float header for _isnan and _finite
Merge pull request #648 from RyanScottLewis/master

Slightly faster Array#each method.
small refactoring for Array#each