Changed sha512 to sha256 to avoid "file name too long" error (issue #51)

* The check for valid sdcard paths has been removed (because it
  doesn't make sense for /dev/sd*, this might as well be a real
  harddrive)
* New check: abort if any partition of the sdcard is mounted
* Automatically detect if the partitions are called "p1", "p2" etc.
  or just "1", "2" etc. (/dev/sda1 vs. /dev/mmcblk0p1)
* pmb.helpers.mount.ismount(): check the source (new) and the target
  path in /proc/mounts

Add samsung-maguro

WIP: Hammerhead kernel config improvements

This reverts commit 04aabd7d.

I did not test this well enough, sorry! This introduced problems
such as interactive shell not working anymore (#40), cryptsetup partion
creating not working anymore etc.

This reverts commit 2a39d9c0.

I did not test this well enough, sorry! This introduced problems
such as interactive shell not working anymore (#40), cryptsetup partion
creating not working anymore etc.

This reverts commit c15bf48f.

I did not test this well enough, sorry! This introduced problems
such as interactive shell not working anymore (#40), cryptsetup partion
creating not working anymore etc.

I did not test this well enough, sorry! This introduced problems
such as interactive shell not working anymore (#40), cryptsetup partion
creating not working anymore etc.

This reverts commit f39c1dae.

Fixed menuconfig with new async runner

Process stdout and stderr from subprocesses separately

Update musl-armhf to r10.

Merging upstream for hammerhead

Merge branch 'device-lg-hammerhead' of github.com:MartijnBraam/pmbootstrap into device-lg-hammerhead