Bug 4427

Description of problem:
urpmi confuses freeed space with added space when removing a big package while upgrading

diff before/after:
 Filesystem Size  Used Avail Use% Mounted on
-/dev/root   95G   74G   21G  79% /
+/dev/root   95G   72G   23G  76% /


Version-Release number of selected component (if applicable):
urpmi-6.43.1-1.mga2

How reproducible:
always

Steps to Reproduce:
1. install an older libreoffice-debug
2. upgrade to a newer libreoffice
3. urpmi reports bogus increase of used disk space:

The following package has to be removed for others to be upgraded:
libreoffice-debug-3.4.99.2-3.mga2.x86_64
 (due to unsatisfied libreoffice-gdb-debug-support == 3.4.99.2-3.mga2) (y/N) To satisfy dependencies, the following packages are going to be installed:
(...)
1.6GB of additional disk space will be used.
209MB of packages will be retrieved.
Proceed with the installation of the 84 packages? (Y/n)