prune-trace: added "sampling with fault expansion"

The FESamplingPruner implements the fault-expansion variance reduction
technique (FE-VRT) as described in: Smith, D. Todd and Johnson, Barry W. and
Andrianos, Nikos and Profeta, III, Joseph A., "A variance-reduction technique
via fault-expansion for fault-coverage estimation" (1997), 366--374.

Change-Id: I04a0c9bb2622974278bd8c73793e51451119e650

tools/prune-trace/CMakeLists.txt

@@ -1,6 +1,7 @@
 set(SRCS
   Pruner.cc
   BasicPruner.cc
+  FESamplingPruner.cc
 )
 
 find_package(MySQL REQUIRED)