[0.13.x] Backport multiple PRs from develop#2688

Merged

codablock merged 3 commits intodashpay:v0.13.xfrom

codablock:pr_v13_backports

Feb 7, 2019

Commits on Feb 6, 2019

Add getspecialtxes rpc (#2668)

UdjinM6
authored and
codablock
committed
Call existsProviderTxConflict after CheckSpecialTx (#2690)
codablock
committed
Change the way invalid ProTxes are handled in `addUnchecked` and `existsProviderTxConflict` (#2691)

UdjinM6
authored and
codablock
committed