two new tools
* cache_dump reads out cache entries and prints them in various orders;
  this is the beginning of a more powerful tool that will be used to
  create output for compiler developers to look at
* reduce is a delta debugger that minimizes souper optimizations
Fix souperweb build
Merge pull request #90 from regehr/tools

two new tools
unconditionally build the clang pass with stats enabled -- by default LLVM turns
off stats for a Release build.  my claim is that the cost of stats is
effectively zero and they're often useful so let's just leave them on.
document the redigo dependency
make "make check" work on MacOS
Merge pull request #93 from regehr/redigo-note

document the redigo dependency
Merge pull request #95 from regehr/mac-fix

make "make check" work on MacOS
optionally ignore solver failures
Merge pull request #94 from regehr/ignore-solver-failure

optionally ignore solver failures
Merge pull request #91 from regehr/pass-stats

unconditionally build the clang pass with stats enabled