Use byte literals to make go vet happy.

The go vet command complains about untagged struct initializers when
defining a ShaHash directly.  This seems to be a limitation where go vet
does not exclude the warning for types which are a constant size byte
array like it does for normal constant size byte array definition.

This commit simply modifies the code to use a constant definition cast to
a ShaHash to overcome the limitation of go vet.
Add go vet back and cleanup travis file.
Add checkpoint at block height 319400.
Changed TxIn.PreviousOutpoint to TxIn.PreviousOutPoint after btcwire API change.
IMPORT PATH MODIFICATION CHANGESET
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Please use this changeset as the first one on top of the conformal codebase.
Note that if there are new imports, they need to be changed as part of this
changeset. In general, use "git rebase" on github.com/conformal's version
and apply this changeset first.