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

1 files changed, 1 insertions, 1 deletions

diff --git a/src/memfile.c b/src/memfile.c
index 497c9ddacd..ee228e6cda 100644
--- a/src/memfile.c
+++ b/src/memfile.c
@@ -192,7 +192,7 @@ memfile_T *mf_open(char_u *fname, int flags)
     unsigned page_size = mfp->mf_page_size;
 
     while (shift > 0 && (page_size & 1) == 0) {
-      page_size = page_size >> 1;
+      page_size /= 2;
       --shift;
     }
     mfp->mf_used_count_max = (p_mm << shift) / page_size;