Bug: .gitconfig folder

[Jorge <griffin@gmx.es>]

If you have a folder named ~/.gitconfig instead of a file with that 
name, when you try to run some global config editing command it will 
fail with a wrong error message:

     "fatal: Out of memory? mmap failed: No such device"


You can reproduce it:

$rm ~/.gitconfig
$mkdir ~/.gitconfig

$ls -la ~
     ...
     drwxr-xr-x 24 hit  hit       4096 may  4 12:30 .gimp-2.8
     drwxr-xr-x  2 hit  hit       4096 may 27 15:26 .gitconfig
     drwxr-xr-x  6 hit  hit       4096 may 27 14:01 github
     ...

$git config --global user.name foo
     fatal: Out of memory? mmap failed: No such device

$git config --global core.editor "vim"
     fatal: Out of memory? mmap failed: No such device