Fix issue with svn copy/move directories.

Fix issue with svn copy/move directories.

svn diff would only generate a diff for modified files but the current code
would not respect full_move=True. full_move=True is necessary to make it work on
the try server.

TEST=svn move chrome chrome2; echo foo>>PRESUBMIT.py
The try job should fail but the diff should be right.
BUG=none

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=46566

[M-A Ruel, 2010-05-04 20:17:39]

Also optimize by reducing the number of "svn info" calls and temporary directory
creations.

[Lei Zhang, 2010-05-04 20:48:39]

http://codereview.chromium.org/1965001/diff/1/2
File scm.py (right):

http://codereview.chromium.org/1965001/diff/1/2#newcode45
scm.py:45: """Generates a fake diff from a file."""
Since we are shuffling code around, can we rewrite this function using cStringIO
instead of string concatenation?

http://codereview.chromium.org/1965001/diff/1/2#newcode682
scm.py:682: def DiffItemInternal(filename, info, bogus_dir, full_move=False,
nit: _DiffItemInternal() ?

http://codereview.chromium.org/1965001/diff/1/2#newcode702
scm.py:702: # This will put a lot of presure on the heap.
s/presure/pressure/

[Lei Zhang, 2010-05-06 00:28:58]

LGTM with small nit.

http://codereview.chromium.org/1965001/diff/7001/4
File scm.py (right):

http://codereview.chromium.org/1965001/diff/7001/4#newcode58
scm.py:58: for l in file_content:
nit: Is that a lower case L? Can you rename the loop variable line>