EXE_DIR dynamic && Fix pushd

Easier pushd, %~dp0% contain the full path to the current runned script ; this avoid the installer to staticly put it in there, removing the new line which make the pushd inoperant.
Remove the static EXE_DIR in gmvauld.bat, this was unclean and buggy (newline removed)

The result was 
SET EXE_DIR=C:\Users\Alexandre\AppData\Local\gmvaultpushd %EXE_DIR%
CR/LF mix in the same file.
The bat now learns where it is located.
Merge pull request #137 from Alex131089/master

Improvement&simplification to gmvault.bat