Increased the multiplier on the timeout test.

It was failing sometimes on my machine.
Uncomment and fix the test of DiffLinesToChars for 300 characters.

The problem was that the input text was being constructed by building lines
using the runes for 1, 2, 3, ... instead of the string representations "1", "2",
"3", .... As a result, the sequence '\n', rune(10), '\n' resulted in a two blank
lines instead of a new, distinct line (since rune(10) == '\n').
Add a test to make sure that a file without a final newline behaves well.
Use assertStrEqual instead of assert.Equal.
Make the DiffCharsToLines text match the python version more closely.
Fixed DiffCleanupSemanticLossless test.

It wasn't using the return value of the function.

Also fixed some utf-8 bugs in the function.
Fixed code and tests for bad utf-8.
Correct comment.
Made diff operation its own type.
changed x[0:y] to x[:y]
ran gofmt
Merge pull request #10 from goojba/tests

Thanks!
Merge pull request #11 from goojba/go-style

Some small changes to the code for better Go style.