Fix a tranche of comment, test and doc typos

llvm-svn: 196510
diff --git a/clang/tools/libclang/CXCompilationDatabase.cpp b/clang/tools/libclang/CXCompilationDatabase.cpp
index 433caec..156a3e2 100644
--- a/clang/tools/libclang/CXCompilationDatabase.cpp
+++ b/clang/tools/libclang/CXCompilationDatabase.cpp
@@ -8,7 +8,7 @@
 
 extern "C" {
 
-// FIXME: do something more usefull with the error message
+// FIXME: do something more useful with the error message
 CXCompilationDatabase
 clang_CompilationDatabase_fromDirectory(const char *BuildDir,
                                         CXCompilationDatabase_Error *ErrorCode)