Assignment operator for maps in NCollection unnecessarily increases buckets array

Map data structures in NCollection share common bug: in operator =, the target
map is resized using number of buckets of source map instead of its actual
content (extent). This leads to the fact that when map is copied, the resulting
map has buckets re-allocated to the next threshold value; this leads to
unnecessary allocation of memory.

The test executable demonstrating this behavior is attached. Its output on
current OCCT is:

:KAS:dev:abvdoc> testmap
Testing NCollection_Map
Initial number of buckets: 101
Copy #0000002: number of buckets = 2003
Copy #4: number of buckets = 10007
Copy #6: number of buckets = 37003
Copy #0000008: number of buckets = 65003
Copy #10: number of buckets = 209953
Copy #12: number of buckets = 995329
Copy #0000014: number of buckets = 995329
Copy #0000016: number of buckets = 995329
Copy #0000018: number of buckets = 995329
Copy #0000020: number of buckets = 995329
Testing TCollection_Map
Initial number of buckets: 101
Copy #0000002: number of buckets = 101
Copy #4: number of buckets = 101
Copy #6: number of buckets = 101
Copy #0000008: number of buckets = 101
Copy #10: number of buckets = 101
Copy #12: number of buckets = 101
Copy #0000014: number of buckets = 101
Copy #0000016: number of buckets = 101
Copy #0000018: number of buckets = 101
Copy #0000020: number of buckets = 101

Note that maps in TCollection does not suffer from such problem.