1) Added a "*showmem" "wizard" command to get a dump of all memory
being used by tiles in the database.
2) Made a slight correction to the way magic detects exact overlap
of instances of the same cell. This probably does not make any
actual difference in practice.
3) Corrected an uninitialized variable in dbReComputeBboxFunc().
4) Changes DBSrCellPlaneArea() to use a static BPEnum variable, so
that it does not waste time allocating and freeing memory for
the same thing over and over again.
5) Corrected a memory leak in the tech file "extract" section that
loses memory every time the extraction style is changed.
6) Corrected the tile join routines to fix a bad memory leak in the
tile allocation and recovery---a fix which was mentioned in issue
#414 but which had not yet been implemented. This has now been
tested and confirmed to work.
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