Update ldraw_import.py

Patch to allow this to work on case-sensitive file systems, (hopefully) without breaking compatibility on case-insensitive file systems
Update ldraw_import.py, removed potential bug, updated TODO

Removed conditional (Lines 607-609)
'if os.path.exists(fname):
   pass'

It has slight potential to cause bugs if Ldraw path is set to a file instead of the Ldraw folder.

Made TODO message on lines 635-636 (hopefully) clearer.
Update ldraw_import.py, Better Error Handling

All outputs to the console now use a debugPrint(STRING) function which is a wrapper for print('[LDraw Importer] '+STRING+' - '+CURRENT_TIME_IN_HOURS:MINUTES:SECONDS)

This makes it easier to determine what messages come from what addons and exactly when they happened.

EXAMPLE 1:
~$: [LDraw Importer] Attempting to import /home/USER/LDCad/plane.ldr - 11:08:46

2. Major error messages now display a small popup when called, notifying the user in Blender's UI, instead of silently closing the file select screen and only outputting to the console.

3. Major Error messages now identify what type of error they were, and print the stack trace where necessary.

EXAMPLE 3:
~$:[LDraw Importer] ERROR: UnicodeDecodeError
Traceback (most recent call last):
  File "ldraw_import.py", line 671, in create_model
    LDrawFile(context, file_name, mat)
  File "ldraw_import.py", line 71, in __init__
    self.parse(filename)
  File "ldraw_import.py", line 169, in parse
    lines = f_in.readlines()
  File "Software/Blender-2.69/2.69/python/lib/python3.3/codecs.py", line 300, in decode
    (result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x90 in position 54: invalid start byte

 - 11:01:18
[Debug] ERROR: File not imported. Reason: UnicodeDecodeError. - 11:01:18

4. Importing files which do not have a .ldr, .dat, or .mpd extension will not be attempted, and will tell the user through a popup in Blender's UI.

EXAMPLE 4:
[Debug] Attempting to import /home/USER/TestZipFle.zip - 11:06:53
[Debug] ERROR: File not imported. Reason: Invalid File Type (Must be a .dat, .ldr, or .mpd) - 11:06:53
Fix indented GPL Header
Replaced a couple single quotes with double quotes, and use spaces instead of tabs.
Update ldraw_import.py to conform to PEP8 Standards

Now conforms to PEP8 Standards, except for some line lengths that are not my code, nor make sense to shorten.
Merge pull request #14 from Tribex/better_errors, closes #14