Squashed commit of the following:

commit 2d7dc0b3
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:22:13 2011 +0200

    Explain more about patches.

commit d5df4cdc
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:18:55 2011 +0200

    Provide better looking patches.

commit c6befb05
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:15:32 2011 +0200

    Support make-command and make-options.

    Fix configure-command.

commit d2212cb7
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:04:05 2011 +0200

    Allow to override configure command.

commit 4321b38a
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:56:49 2011 +0200

    Share applyPatchList with in base class.

commit 4a2ea3b3
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:56:29 2011 +0200

    Support no md5sum.

commit 2cd36cb7
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:56:16 2011 +0200

    Show how to patch.

commit 8cd9ea9c
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:53:45 2011 +0200

    Allow options per patch.

commit 84fea623
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:48:47 2011 +0200

    Allow patching.

commit 8934eb92
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:30:46 2011 +0200

    Allow to keep directories in case of error.

    Default is to remove.

commit 74d0b2bd
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:24:49 2011 +0200

    Allow to have a=b=c, where a is key and b=c is value.

commit 034c2381
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:17:07 2011 +0200

    Another typo.

commit f5abcde0
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:15:44 2011 +0200

    Follow fixed typo.

commit 5b950e26
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:14:35 2011 +0200

    Extract does not need md5sum.

commit 6f725632
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:14:14 2011 +0200

    Pass md5sum directly.

commit 9f42d22a
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:13:53 2011 +0200

    Allow to pass empty md5sum.

commit c91fafb1
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:13:15 2011 +0200

    Fix typos.

commit 8919378d
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:12:31 2011 +0200

    Fix examples.

Fix configure-command.

Default is to remove.

slapos.cookbook provided it before, but it is simple functionality, which does
not need so many dependencies.

Additionaly support slapos_update_promise

pipeCommand allows to simulate shell pipes.

failIfPathExists allows to stop in case of path which exists.

Read md5sum passed to method directly.