Add dedicated pretty-printer tests with new pp-exact directive

Add a new src/test/pretty directory to hold just source files for testing the
pretty-printer.

Add a new pp-exact directive. When this directive is followed by a file name
it specifies a file containing the output that the pretty-printer should
generate. When pp-exact is not followed by a filename it says that the file
should pretty-print as written.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/test/pretty/example2.rs b/src/test/pretty/example2.rs
new file mode 100644
index 00000000000..3f3e99a49a8
--- /dev/null
+++ b/src/test/pretty/example2.rs
@@ -0,0 +1,7 @@
+// pp-exact:example2.pp
+
+fn
+main
+()
+{
+}
\ No newline at end of file