Merge pull request #76 from bgilbert/valgrind

docs/testsuite: re-add valgrind command

docs/testsuite/index.md

@@ -21,6 +21,11 @@ Sanitize mode requires:
 - clang
 - Debug symbols for library dependencies (particularly glib2) and Fontconfig
 
+Valgrind mode requires:
+
+- Valgrind
+- Debug symbols for library dependencies (particularly glib2) and Fontconfig
+
 Coverage mode requires:
 
 - gcov
@@ -43,6 +48,11 @@ etc., but is somewhat slow.
 
     ./driver sanitize
 
+You can also run the test cases under Valgrind.  This will catch memory
+leaks, invalid memory accesses, double frees, etc.  It is also very slow.
+
+    ./driver valgrind
+
 To generate a test coverage report:
 
     ./driver coverage out.txt
@@ -65,8 +75,9 @@ the desired directory path.
 
 On some platforms, certain test cases may fail due to problems in other
 libraries.  To prevent those cases from cluttering the test report, you can
-set the `OPENSLIDE_TEST_XFAIL` environment variable to a comma-separated
-list of cases which are expected to fail.
+set the `OPENSLIDE_TEST_XFAIL` and/or `OPENSLIDE_VALGRIND_XFAIL` environment
+variables to a comma-separated list of cases which are expected to fail
+during `run` or `valgrind`, respectively.
 
 ### Using a local mirror