Merge lp://staging/~bcbc/wubi/lp694242 into lp://staging/wubi

This patch lets Wubi check whether Windows boots using EFI and, if so, prevents further processing.

The technique used is to examine the output of BCDEDIT for the presence of either bootmgfw.efi or winload.efi. I'm not entirely happy with this technique: ideally there would be a registry entry that is conclusive, but it works on BCDEDIT output I've seen from EFI systems ( http://ubuntuforums.org/showthread.php?t=2070760&p=12296995&viewfull=1#post12296995 )

The check is performed prior to making any changes, so there is no need to download anything or uninstall once it has been determined that Windows boots in is in EFI mode.

I have tested this patch to confirm that it installs as usual on BIOS firmware (tested on Windows XP and Windows 8).
I haven't tested it on an EFI computer as I don't own one, but I created a test version that was identical except it searched for a string that happened to exist in my BCDEDIT output.
Ideally, we could build the wubi-r280.exe and then make a call for some community testing to confirm positive tests.

The wubi-13.04-rev280.log file contains the additional line if not using EFI:
04-22 21:51 DEBUG WindowsBackend: EFI boot = False

or if using EFI the following lines:
04-22 21:51 DEBUG WindowsBackend: EFI boot = True
...
04-22 21:51 ERROR root: Wubi does not currently support EFI

There is also a Windows popup with the message: Wubi does not currently support EFI