If the git config setting diff.mnemonicprefix is set, that causes git
diff to use prefixes that indicate what is being compared rather than
always using "a" and "b". For the way that meld invokes git diff, the
prefixes will always be "c" for commit (HEAD) and and "w" for the work
tree. This confuses the patch parser and prevents the modified files
from being copied to the temporary directory, which then results in
patch failing to reverse the changes.

This patch fixes this by modifying the regular expression used to find
index entries in the patch to accept "c" and "w" as prefixes as well as
"a" and "b".

Scrolling through commits using the keyboard shows up the translation
of the line/column and overwrite labels as unusually expensive calls.
This patch eliminates this overhead by caching the translated strings.

Neither git diff-index nor name-status give us information about
untracked files within git. This commit adds an additional ls-files
call to obtain a list of untracked/unversioned files.

For the purpose of syntax highlighting, we always try to determine the
mime type of files, currently using only the filename. In situations
where the filename tells us nothing, we can reasonably assume that all
files have the same type.

This commit changes our behaviour so that, if we get one useful file
type, we use it to fill in missing file types in the remaining files.
This should specifically help with cases where temporary files are
given different extensions. e.g., TortoiseSVN uses .mine, .working, etc.

Because chunk actions insert, delete or change large quantites of text,
these actions can cause the reader to temporarily lose their place in
the text. This commit adds some very simple animation providing visual
cues showing the effects of actions on diff chunks.

The check for a checkpointed (i.e., saved) buffer was incorrect for the
very first undo in a sequence. Due to a None-handling mishap, a
checkpoint that should have ranged from 0:0 always ranged from 0:1.