[lib] Creation of I/O decorated functions.
[pep8] Fix some trailing spaces, >80chars lines, etc.
[core] Check if tmp logfile exists before reading from it.
[owtf] Revert previous permissions checking function.

Reverted commits:

+ 5c410e9def6985daa3928037d510104bae373836
+ 7aef0248d7b9f8c157279faad360482a6ff8c572
+ 3157669da1b4dfe331f2b146f4879244912a7dec
+ 71df07b018a218b2fbde441f7b10d9ab1fd0a601
(Fix #242) Force OWTF to use i/o decorators.

The decorated i/o functions will properly exit OWTF if a perm error is raised
when opening/reading/creating files/directories.

**Discussion**

Maybe the `open()` function should be decorated. What do OWTF contrib think?