buildroot

check-package: check whitespace and empty lines

Create 3 new check functions to warn when:
- there are consecutive empty lines in the file, see [1];
- the last line of the file is empty, see [2];
- there are lines with trailing whitespace, see [3].

Apply these functions to Config.*, *.mk and *.hash, but not for *.patch
files since they can contain any of these and still be valid.

[1] http://patchwork.ozlabs.org/patch/682660/
[2] http://patchwork.ozlabs.org/patch/643288/
[3] http://patchwork.ozlabs.org/patch/398984/

Signed-off-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>