git: Bring in a simple event tracing library and POC utility

[Matthew Dillon]

    I can definitely see standardizing the format strings, at least
    well enough that they can be parsed out and accumulated for
    statistical purposes.

    The bigger problem right now is KTR for 64-bit.  We can't use
    vaargs due to the massive overhead the 64-bit varargs code uses,
    so we need to some up with a better KTR API, maybe one with different
    macros each taking a different number of argumetns so we can
    efficiently generate the KTR entries.

					-Matt