Add "Full" diff context option for showing complete file source

When using the internal diff to view changes it would be useful to have an option to see the entire contents of a file, rather than being limited to 100 lines of context. Sometimes a piece of code related to a given change is outside the range of 100 lines, and it would be nice to be able to switch to see the entire file contents, as is possible in the Fisheye diff viewer.

In addition, it's convenient to be able to use the File Status / Working Copy view as a quick, light code browser. However, when viewing file contents, larger files are cut off after 100 lines, so that either Quick Look or another editor has to be launched to see the full source.