#479 Minor optimisation to BinaryProc

[afredd]

Replacing the for loop in BinaryProc (which is used
to copy characters from one buffer to another) with
a memcpy provides a minor speed up.

Justication:
BinaryProc is often used on channelBuffer's
ie. srcLen is often 4096, and memcpy is much quicker
than a for loop in such cases (i measure it at
about 10x).

It seems like a memcpy() is faster that a for loop
whenever more than ~16 characters are copied, which
is probably the most common case in calls to
BinaryProc.

[afredd]

Patch to tclEncoding

[Don Porter]

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looks fine to me; tests ok.
memcpy() already used
throughout Tcl sources.

committed to both active
branches.