direct.stdpy.file tell() can cause exceptions, and lacks 'with' support

[Craig Macomber]

from direct.stdpy import file
file.open('test.txt','wb').tell()

"""
Causes this error:
Traceback (most recent call last):
  File "test.py", line 2, in <module>
    file.open('test.txt','wb').tell()
  File "/Developer/Panda3D/lib/direct/stdpy/file.py", line 218, in tell
    raise ValueError
ValueError
"""

with file.open('test.txt','wb') as f:
    pass

"""
Causes this error:
Traceback (most recent call last):
  File "/Users/Craig/Desktop/test.py", line 14, in <module>
    with file.open('test.txt','wb') as f:
AttributeError: file instance has no attribute '__exit__'
"""

# direct.stdpy.file does not support tell() in some cases (perhaps just before any reading or writing?)
# direct.stdpy.file does not support being used with 'with' blocks
# these are supported by python's file objects,
# and losing these features when the runtime replaces the builtin open method can
# cause confusing and annoying issues

# Tested on Mac OS 10.5 and 10.6 (intel) with panda 1.7.0

[David Rose (droklaunchpad)]

First bug fix committed as version 1.13 of file.py.

Second bug was previously reported and already fixed on trunk.