--WITH-MAX-INDEXES=128

The MySQL server bitmap implementation defines two
template Bitmap classes. One optimized for 64-bit
(default) wide bitmaps while the other one is used for
all bitmaps with non-default width.

In order to optimize the computations, Bitmap<64> class
has defined its own member functions for bitmap operations,
the other one, however, relies on mysys' implementation of
bitmap (mysys/my_bitmap.c).

Issue 1:
In mysys bitmap implementation, while setting the prefix
bits, an extra byte beyond the bitmap buffer can be set
to 0. Now, as this piece of code is used only for bitmaps
with non-default width, the issue wasn't visible in the
64-bit wide (default) builds.

Fixed the offending mysys bitmap function by properly
adjusting the number of prefix bytes, which is used to
bzero the remaining bitmap buffer.

Issue 2:
In case of non-default Bitmap class, the intersect function
wrongly resets the received bitmap while initialising a new
local bitmap structure (bitmap_init() clears the bitmap
buffer) and hence the received bitmap was getting lost.

Fixed by initializing the local bitmap structure by using a
temporary buffer and later copying the received bitmap
to the initialised bitmap structure.

Also added a cmake variable to hold the MAX_INDEXES
value when supplied from the command prompt.
(eg. cmake .. -DMAX_INDEXES=128U). Checks has been put
in place to trigger a build failure if MAX_INDEXES value
is greater than 255.

Test modifications:
* Introduced include/have_max_indexes_[64|128].inc to
  facilitate skipping of tests for which the output
  differs with different MAX_INDEXES.

* Introduced include/max_indexes.inc which would get
  modified by cmake to reflect the MAX_INDEXES value
  used to build the server. This file simply sets an
  mtr variable '$max_indexes' to show the MAX_INDEXES
  value, which will then be consumed by the above
  introduced include file.

* Some test's outputs were dependent on MAX_INDEXES
  value, they have been moved to new test files.

* Added gunit tests for the fixed issues.