Use /2 and 2* instead of >>1 and <<1 which are tricky with signed types

Today's compilers generate shift instructions to perform division and
multiplications by powers of 2 [1]. `(x >> 1)` looks straightforward enough, but
if x is signed the code will fail when x < 0. The compiler knows better: use
`x / 2`.

That's why we have code like this:

    (long)((long_u)Rows >> 1))

instead of the cleaner version that generates the same or better machine code:

    Rows / 2

[1] http://goo.gl/J4WpG7

src/quickfix.c

@@ -312,7 +312,7 @@ qf_init_ext (
   /*
    * Get some space to modify the format string into.
    */
-  i = (FMT_PATTERNS * 3) + ((int)STRLEN(efm) << 2);
+  i = 3 * FMT_PATTERNS + 4 * (int)STRLEN(efm);
   for (round = FMT_PATTERNS; round > 0; )
     i += (int)STRLEN(fmt_pat[--round].pattern);
 #ifdef COLON_IN_FILENAME