build: fix typo in configure help message

--with-qt-libdir etc, not --with-gui-libdir.
The typo was introduced in a9dbcf036bc866c2e413b1d068541e35eafdfcd0.
Typesafe strprintf/error/LogPrint functions

Switch to tinyformat-based formatting.

Tinyformat is a typesafe drop-in replacement for C99 printf functions:
https://github.com/c42f/tinyformat
Remove redundant .c_str()s

After the tinyformat switch sprintf() family functions support passing
actual std::string objects.

Remove unnecessary c_str calls (236 of them) in logging and formatting.
Merge pull request #3549

7d9d134 Remove redundant .c_str()s (Wladimir J. van der Laan)
b77dfdc Typesafe strprintf/error/LogPrint functions (Wladimir J. van der Laan)
ui: Clarify help messages for 'message' fields

Add or amend tooltips to clarify what the message is for and that it
doesn't go over the network.
Merge pull request #3571

57feb1b ui: Clarify help messages for 'message' fields (Wladimir J. van der Laan)
Unit test fixes for AssertLockHeld / -DDEBUG_LOCKORDER

Unit tests would fail if compiled with -DDEBUG_LOCKORDER (AssertLockHeld()
would fail; AssertLockHeld() relies on the DEBUG_LOCKORDER code to keep
track of locks held).

Fixed by LOCK'ing the wallet mutex in the unit tests that manipulate the
wallet.
Merge pull request #3578 from gavinandresen/unittest_debuglockorder

Unit test fixes for AssertLockHeld / -DDEBUG_LOCKORDER