Fix problem with .options file and extension fields.

The options for an extension field were being looked up under wrong name
(MessageName instead of MessageName.fieldname).

Fixed the problem and added regression test. Created a new subfolder for
regression test cases.

Update issue 125
Status: FixedInGit
Give better messages about the .options file path.

Update issue 124
Status: FixedInGit
Do not automatically add a dot with generator -e option.

Now -e option in generator is more versatile. Especially it avoids
double-dot problem with some build systems.

Given foobar.proto, we now get:
-e .pb  =>  foobar.pb.c (default)
-e _pb  =>  foobar_pb.c
-e ''   =>  foobar.c

Note that if you have used -e option previously, you will have to prepend
. to the argument to get the same filenames as before.

Update issue 122
Status: FixedInGit
Cleanup and comment the code of network_server example.

Update issue 123
Status: FixedInGit
Add support for inverted patterns in test framework.
Add skip_message option to generator.

Update issue 121
Status: FixedInGit