Add another scripts search path for Windows builds

Add another scripts search path for Windows builds

Add single "scripts" folder to search path for Windows OpenOCD builds
that don't use cygwin
bin/openocd.exe
scripts/interface/dummy.cfg
scripts/target/at91eb40a.cfg

Do some refactoring of current code (thx to Andreas).

Change-Id: Idbb08d1368b06f25da44f4f9ab1511db992b1724
Signed-off-by: Freddie Chopin <freddie.chopin@gmail.com>
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/785
Tested-by: jenkins