QDir::tempPath: clarify trailing-slash situation.

tst_QDir::tempPath already checks that there is no trailing slash.
Except of course when the path is "/" or "C:/", but we can't do much
about that unlikely corner case.

Change-Id: If71d5de1aeebc6720348cecbf659b7fceb83fb0e
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/corelib/io/qdir.cpp

@@ -1944,8 +1944,8 @@ QString QDir::homePath()
     On Unix/Linux systems this is the path in the \c TMPDIR environment
     variable or \c{/tmp} if \c TMPDIR is not defined. On Windows this is
     usually the path in the \c TEMP or \c TMP environment
-    variable. Whether a directory separator is added to the end or
-    not, depends on the operating system.
+    variable.
+    The path returned by this method doesn't end with a directory separator.
 
     \sa temp(), currentPath(), homePath(), rootPath()
 */