[PATCH] Speed-up of libsvn_diff by reworking fp argument

[[[
Faster LCS algorithm in libsvn_diff by reworking fp argument

* subversion/libsvn_diff/lcs.c
  (svn_diff__snake): fp and k arguments are added by caller
]]]

Calling svn_diff__snake with fp+k as argument instead of both as
separate arguments reduces running time for the lcs algorithm
substantially; by more than 20% on my system. Combining this
patch with the idx one gives a slight additional speed
improvement, but not nearly the sum of each separate
improvement (on my system, at least).

Patched version produces identical diff results and passes
all libsvn_diff tests.

Should I maybe change the name of fp in svn_diff__snake?

Morten