Fix subprocess watching.

Currently, the subprocess watching code polls with a delay between attempts.
Instead, introduce wait_with_timeout() and use it, simplifying this code.

Signed-off-by: Elly Fong-Jones <[email protected]>
diff --git a/CHANGELOG b/CHANGELOG
index fbe7a83..c408a15 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -15,6 +15,7 @@
   Add Mac OS X 10.8.3 support
   Extensive setup/install documentation is now present in INSTALL for most OSes
   Add DragonFly BSD 3.3 support
+  Refactored subprocess watching.
 0.0.6 Mon 18 Feb, 2013
   Ensure that tlsdate compiles with g++ by explicit casting rather than
   implicit casting by whatever compiler is compiling tlsdate.