Fixes #4002: Move r29988 to v1.7 branch (fix topo _map function pointer assignments)

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r29988 [[BR]]
Remove the comments around these assignments; otherwise, we won't get
function pointers set to the _map functions, and we get segv's in MTT
testing (e.g., the C++ suite, which actually calls MPI_Cart_map and
MPI_Graph_map).

cmr=v1.7.4:reviewer=bosilca:subject=Fix topo _map function pointer assignments
Fixes #4001: Move r29987 to v1.7 branch (Fix missing include of show_help.h)

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r29987 [[BR]]
Fix missing include of show_help.h in mtl mxm.

cmr=v1.7.4:reviewer=jsquyres
Fixes #4009: Move topo base uninit var fix to v1.7

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r29030 [[BR]]
Avoid segfault due to uninitialized variable
Fixes #4008: Move r29998 to v1.7 branch (Add missing include file.)

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r29998 [[BR]]
Add missing include file.

Thanks to Paul Hargrove for spotting it.

cmr=v1.7.4:reviewer=jsquyres