Correct and expand documentation of splitLocale()

This amends c1141ed729b84f2c413975d37c1a91fb235fb14a; I failed to
update the doc-string after some design changes part-way through
developing the function.

Change-Id: Ifb83107153d1c3b5a9dbd0536a3d6ee1fe32922d
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@qt.io>

util/local_database/cldr2qlocalexml.py

@@ -446,8 +446,10 @@ def integrateWeekData(filePath):
 def splitLocale(name):
     """Split name into (language, script, territory) triple as generator.
 
-    Ignores any trailing fields, leaves script or territory empty if
-    unspecified, returns empty generator if no language found."""
+    Ignores any trailing fields (with a warning), leaves script (a capitalised
+    four-letter token) or territory (either a number or an all-uppercase token)
+    empty if unspecified, returns a single-entry generator if name is a single
+    tag (i.e. contains no underscores).  Always yields 1 or 3 values, never 2."""
     tags = iter(name.split('_'))
     yield tags.next() # Language
     tag = tags.next()