* src/util/bitmap.c (virBitmapAlloc): Tighten sanity check.

V2:
  - Move bitmap impl to src/util/bitmap.[ch]
  - Use CHAR_BIT instead of explicit '8'
  - Use size_t instead of unsigned int
  - Fix calculation of bitmap size in virBitmapAlloc
  - Ensure bit is within range of map in the set, clear, and get
    operations
  - Use bool in virBitmapGetBit
  - Add virBitmapFree to free-like funcs in cfg.mk

V3:
  - Check for overflow in virBitmapAlloc
  - Fix copy and paste bug in virBitmapAlloc
  - Use size_t in prototypes
  - Add ATTRIBUTE_NONNULL in prototypes where appropriate
    and remove NULL check from impl

V4:
  - Add ATTRIBUTE_RETURN_CHECK in prototypes where appropriate.