Don't mess the quickfix window when checking for android.

Use of vimgrep to find the android target version messes the quickfix window.
This causes the quickfix window to be replaces during compiles and files
searches when working in Java.

Instead use readfile to read the properties file and scan it to find the desired
target version.
Improve the quickfix auto open option.

- Open the quickfix window if there are errors in it.
- Close it when empty.
- Make sure it always opens at the bottom of the window. This fixes the case
  when TagBar or TagList are open causing the quickfix window to be opened below
  them.