Explain about the automated tests on Travis

in order to advise contributors to locally test their patches.

Also update ctest to include a fix on rerun-if-changed so that human
developers doing trial & error can properly test their latest code.

Signed-off-by: NODA, Kai <nodakai@gmail.com>

README.md

@@ -88,6 +88,16 @@ With that in mind, the steps for adding a new API are:
 4. Wait for CI to pass, fixing errors.
 5. Wait for a merge!
 
+### Test before you commit
+
+We have two automated tests running on [Travis](https://travis-ci.org/rust-lang/libc):
+
+1. [`libc-test`](https://github.com/alexcrichton/ctest)
+  - `cd libc-test && cargo run`
+  - Use the `skip_*()` functions in `build.rs` if you really need a workaround.
+2. Style checker
+  - `rustc ci/style.rs && ./style src`
+
 ## Platforms and Documentation
 
 The following platforms are currently tested and have documentation available:

libc-test/Cargo.lock

@@ -14,7 +14,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 [[package]]
 name = "ctest"
 version = "0.1.0"
-source = "git+https://github.com/alexcrichton/ctest#50ac771acb7bb45cf0c182a5a9c8188a15c89efc"
+source = "git+https://github.com/alexcrichton/ctest#a6becb6d7fd23d9863cba86eac31d1ffc4082734"
 dependencies = [
  "gcc 0.3.25 (registry+https://github.com/rust-lang/crates.io-index)",
  "syntex_syntax 0.19.1 (registry+https://github.com/rust-lang/crates.io-index)",