kmk: Add suuport TOOL property to tasks unit.

This may be used in COMMAND(S) to refer to a file from the source tree
used in the execution process (e.g. a script).
kmk: Speed up kmk configure.

This is done by skipping inclusion of all make files but the root one.
kmk: Build xpconnect libraries.
kmk: Build security/manager libraries.
kmk: Print name of the included makefile while going through subdis.

This is to give the user some feedback (useful if there are many files).
kmk: js: Use DLL_SUFFIX/DLL_PREFIX.