Workaround for missing Content-Length information

Under some scenarios, certain webservers or proxies will miss
the `Content-Length` header that is used by the progress bar
component, causing the download task to abort.

This workaround was promosed in the mailing list and is hard to
reproduce.
Upgrade RubyGems to version 1.8.29

This one is used by Ruby 1.8.x and 1.9.x so an update to latest
available in the 1.8.x series was recommended.
Upgrade Ruby 2.0.0 to patchlevel 576

Results of `make check`:

https://gist.github.com/luislavena/242bfe198d4ec7e7a69b
Update Ruby 2.1 to version 2.1.3

Results of `make check`:

https://gist.github.com/luislavena/3ca45d084dea3f4c6667
Prepare releases
Use msys2(32bit) instead of old msys

Parallel make hangs due to msys bug.
http://sourceforge.net/p/mingw/bugs/1950/

msys2 is updated version of msys and the bug seems to be fixed.
http://mingw-users.1079350.n2.nabble.com/Status-of-MSYS2-td7582391.html

We pick up msys2 minimal dependencies to build ruby.
Need to set MSYSTEM=MINGW32 environment variable.

Default value of MSYSTEM is changed with msys2.
http://sourceforge.net/p/msys2/tickets/4/
Pass make options by MAKE_OPT environment variable

We can pass -jN to make for build speedup.
Replace mingw/gnuwin32 packages to msys2
Add /etc/fstab to remove cygdrive prefix

`/cygdrive` prefix may cause failures of installing gems.
Bump msys2 2.0.16196.25874b1-1-i686

- `sh.exe` crashes with latest `msys2-runtime` for some reason.
  We add filesystem package to fix `sh.exe` crash.

- remove `resources/devkit/fstab` since filesystem package
  contains `/etc/fstab`.

- keep msys2 default `/usr/bin` path to work properly.
  We modify PATH environment variable of devkit settings.

- `msys-unistring-2.dll` causes an error at fork while buiding ruby.
  We run rebase `msys-unistring-2.dll` to fix the error.
Upgrade to latest msys2 packages

This includes bash CVE fixes.