Include the "ipython3" command for IPython

In certain types of Linux packaging, the command for the IPython interpreter may be named "ipython2" and/or "ipython3" rather than simply "ipython" to distinguish Python 2.x and 3.x interpreter versions.

guake/prefs.py

@@ -64,7 +64,7 @@
 
 # A regular expression to match possible python interpreters when
 # filling interpreters combo in preferences (including bpython and ipython)
-PYTHONS = re.compile(r"^[a-z]python$|^python\d\.\d$|^python\d\.\d\d$")
+PYTHONS = re.compile(r"^[a-z]python$|^[a-z]python\d$|^python\d\.\d$|^python\d\.\d\d$")
 
 # Path to the shells file, it will be used to start to populate
 # interpreters combo, see the next variable, its important to fill the