[analyzer] Minor fixes and improvements to debug.ExprInspection

- Fix the bug with transition handling in ExprInspectionChecker's
  checkDeadSymbols implementation.

- Test this bug by adding a new function clang_analyzer_numTimesReached() to
  catch number of passes through the code, which should be handy for testing
  against unintended state splits.

- Add two more functions should help debugging issues quickly without running
  the debugger or dumping exploded graphs - clang_analyzer_dump() which dump()s
  an SVal argument to a warning message, and clang_analyzer_printState(), which
  dump()s the current program state to stderr.

Differential Revision: https://reviews.llvm.org/D26835

llvm-svn: 288257