[conformal/btcchain] ff4d01: Split time too old error into two distinct errors.

[Dave Collins]

  Branch: refs/heads/master
  Home:   https://github.com/conformal/btcchain
  Commit: ff4d01765f6e853ad826d36a87424312797bc331
      
https://github.com/conformal/btcchain/commit/ff4d01765f6e853ad826d36a87424312797bc331
  Author: Dave Collins <da...@conformal.com>
  Date:   2014-07-11 (Fri, 11 Jul 2014)

  Changed paths:
    M error.go
    M error_test.go
    M process.go

  Log Message:
  -----------
  Split time too old error into two distinct errors.

This commit splits the two rule validation errors related to the timestamp
being too old into two distince errors rather than grouping them under the
same one.  Thus there is now a new ErrCheckpointTimeTooNew in addition to
the existing ErrTimeTooNew error.

This allows the caller to detect the when a block is rejected due to a
time-related checkpoint failure whereas before the combined error did not.