Release 1.5.2

Almost a major release, with some cool new feature. But the release 1.6 will be reaaally cool!

Features

add command CU (commit undo) to close commit section (fix #55)
add g:magit_discard_untracked_do_delete option (fix #66)
when set, discard an untracked file will actually delete this file
support 'typechanged' git status type

clear undo history after each update_buffer() call (refs #64)
undo in magit buffer did the user believe that it may undoes some vimagit
actions: it is not! magit buffer undo history is wiped at each refresh;
which means undo still works while the user is typing its commit message
for example.
binary file detection is done with git diff (fix #60, #61)
it fixes false positive binary file detection, binary file detection on
Windows, and may eventually speed up the refresh process :)
output an understandable message when user tries ot discard an untracked file (fix #58)
remove unwanted --No lines in buffer-- in status line when opening magit buffer (fix #56)
use 'diff -p' instead of 'diff --patch' (fix #52)
better handling of some command line error code and improve some error messages
set local foldnestmax (fix #62)