Memoization of scev in DiracTrick should be controlled
by MemSet.
Memoization of dcheck in DiracTrick should be controlled
by MemSet
Ensured that memoization in DiracTrick doesn't prevent us switching
gamma^5 schemes on the fly.
Removed unused arguments in some definitions of DiracTrick.
Refactored some relations in DiracTrace that involve fermion propagators
and projectors in a chain of Dirac matrices and ensured that they are
applied only in four dimensions or in a naive gamma^5 scheme.
Added some explanatory comments to the source code of DiracTrick.
Improved the handing of the chirality projectors in non-naive gamma^5 schemes in DiracTrick.
Reworked the handling of contractions of Dirac matrices in D, 4 and
D-4 dimensions in DiracTrace.
Added simplification of Dirac matirx chains where the two contracted
matrices are in different dimensions.
Added simplifications of g^mu g^nu_1 ... g^nu_n g_mu where g^mu is in 4
and g^nu_i are in D-4 dimensions or vice versa.
Reworked simplification of g^mu g^nu g_mu where g^mu and g^nu can
be in D, 4 or D-4 dimensions.
Reworked simplification of g^mu g^nu g^rho g_mu where g^mu and g^nu g^rho
can be in D, 4 or D-4 dimensions.
Reworked simplification of g^mu g^nu g^rho g^sigma g_mu where g^mu and
g^nu g^rho g^sigma can be in D, 4 or D-4 dimensions.
Reworked simplification of g^mu g^nu g^rho g^sigma g^tau g_mu where
g^mu and g^nu g^rho g^sigma g^tau can be in D, 4 or D-4 dimensions.
Added some comments are moved few functions to different locations in
DiracTrick.
Reworked simplification of g^mu g^nu g^rho g^sigma g^tau g^kappa g_mu where
    g^mu and g^nu g^rho g^sigma g^tau g^kappa can be in D, 4 or
D-4 dimensions.
Reworked simplification of g^mu g^i_1 ... g^i_n g_mu, where all matrices
are in 4 dimensions.
Reworked simplification of
g^mu g^i1 .... g^in g_mu, where all matrices are in D-4 dimensions
Added simplifications for for g^mu g^nu_1 ... g^nu_n g_mu where g^mu
is in D and g^nu_i are in 4 dimensions.
Added simplification for g^mu g^nu_1 ... g^nu_n g_mu where g^mu is
in D and g^nu_i are in D-4 dimensions.