Tidy up CRYPTO_EX_DATA structures.

DSA_METHOD to make it more consistent with RSA_METHOD.

while implementing and using it.

Submitted by:
Reviewed by:
PR:

1. The already released version was 0.9.1c and not 0.9.1b

2. The next release should be 0.9.2 and not 0.9.1d, because
   first the changes are already too large, second we should avoid any more
   0.9.1x confusions and third, the Apache version semantics of
   VERSION.REVISION.PATCHLEVEL for the version string is reasonable (and here
   .2 is already just a patchlevel and not major change).
tVS: ----------------------------------------------------------------------