QGit: Shrink used memory with custom git log format

["Marco Costalba" <mcostalba@gmail.com>]

Hi all,

   I have pushed a patch series to

git://git.kernel.org/pub/scm/qgit/qgit4.git

that changes the format of git log used to read data from a git repository.

Now instead of --pretty=raw a custom made --pretty=format is given,
this shrinks loaded data of 30% (17MB less on Linux tree) and gives a
good speed up when you are low on memory (especially on big repos)

Next step _would_ be to load log message body on demand (another 50%
reduction) but this has two drawbacks:

(1) Text search/filter on log message would be broken

(2) Slower to browse through revisions because for each revision an
additional git-rev-list /git-log command should be executed to read
the body

The second point is worsted by the fact that it is not possible to
keep a command running and "open" like as example git-diff-tree
--stdin and feed with additional revision's sha when needed. Avoiding
the burden to startup a new process each time to read a new log
message given an sha would let the answer much more quick especially
on lesser OS's

Indeed there is a git-rev-list --stdin option but with different
behaviour from git-diff-tree --stdin and not suitable for this.

Marco