magit.el: execute git grep on toplevel directory

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
magit.el: use word-at-point as default input to grep

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Merge commit '25b5f6e3ca7f9892ce607121aaf5c4409b994b19' into artagnon/grep
fix byte-compilation
Merge branch 'artagnon/grep'
Merge remote-tracking branch 'origin/master'
Using just emaclient as editor if server-name is the default value.

Otherwise there are problem on windows (Closes #497)
There is still a problem with non standard server name on windows, but
this commit fix most common case.
Merge branch 'mainline-maint' into mainline-master
fix travix make targets
Merge branch 'maint'
Merge branch 'maint' of github.com:magit/magit into maint
Merge branch 'master' of github.com:magit/magit
Merge branch 'maint'
fix travix make targets
Merge branch 'maint'