build: fix release name strings for gitian builds

When building from a distdir as gitian does, checking for the .git dir
is not reliable. Instead, ask git if we're in a repo.
Fixing improper input syntax and failing bounds check
remove code below asserts in limitedmap.h (fixes a ToDo)
Use actually valid transactions for script tests
Add actual signature tests
[Qt] minor changes in splashscreen.cpp

- guard an unused variable with Q_UNUSED() macro
- remove a commented out line of code
Grammar fixes in README

Github-Pull: #4956
Fixing out of bounds error in GetKey()
Merge pull request #4962

6f3ae9b Fixing out of bounds error in GetKey() (ENikS)
Merge pull request #4949

c8589bf Add actual signature tests (Pieter Wuille)
76ec867 Use actually valid transactions for script tests (Pieter Wuille)
Fixing out of bounds asses error
Avoiding referencing elements of an empty vector
Merge pull request #4955

87314c1 Fixing improper input syntax and failing bounds check (ENikS)
Reinitializing list's begin iterator after few elements were erased from the head
Fixed typo in README.md file. "-regest" "-regtest"

There was a typo in the README.md file. It previously read "-regest" instead of the proper "-regtest" and it has been updated to the proper reading.
Merge pull request #4974

b498a94 Fixed typo in README.md file. "-regest" "-regtest" (Eric Shaw)
[Qt] add more NULL pointer checks in bitcoingui

- add missing checks for clientModel and optionsModel
- small cleanups for an #ifdef on Mac
- remove an unneeded else
Merge pull request #4958

e6beedc [Qt] add more NULL pointer checks in bitcoingui (Philip Kaufmann)
RPC getnetworkinfo: export local node's client sub-version string
Merge pull request #4914

ff36cbe RPC getnetworkinfo: export local node's client sub-version string (Jeff Garzik)