adding tests/ directory per build.xml settings

Hi Mac, a fresh checkout produces the following error. So I've added the test/ directory, with a .gitignore since we don't yet have any tests to run. Another option would be to pull the testing steps out of the build.xml, but my ant/java is very weak, and we may at some point want to add tests. :)

```
teamcity@hsv:~/teamcity_campfire_notifier$ ant
Buildfile: /home/teamcity/teamcity_campfire_notifier/build.xml

clean:
   [delete] Deleting directory /home/teamcity/teamcity_campfire_notifier/build

dir.build:
    [mkdir] Created dir: /home/teamcity/teamcity_campfire_notifier/build

compile:
    [mkdir] Created dir: /home/teamcity/teamcity_campfire_notifier/build/classes
    [javac] /home/teamcity/teamcity_campfire_notifier/build.xml:45: warning: 'includeantruntime' was not set, defaulting to build.sysclasspath=last; set to false for repeatable builds

BUILD FAILED
/home/teamcity/teamcity_campfire_notifier/build.xml:45: srcdir "/home/teamcity/teamcity_campfire_notifier/tests" does not exist!

Total time: 0 seconds
```

Here is a little info about the environment & tools:

```
Linux hsv 3.11.0-15-generic #25~precise1-Ubuntu SMP Thu Jan 30 17:39:31 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

java version "1.6.0_27"
OpenJDK Runtime Environment (IcedTea6 1.12.6) (6b27-1.12.6-1ubuntu0.12.04.4)
OpenJDK 64-Bit Server VM (build 20.0-b12, mixed mode)

Apache Ant(TM) version 1.8.2 compiled on December 3 2011
```