Fixed ant build files for Android project.

briar-android/.gitignore

+bin
+gen
+res
+local.properties

briar-android/ant.properties

@@ -9,6 +9,9 @@
 #  'source.dir' for the location of your java source folder and
 #  'out.dir' for the location of your output folder.
 
+source.dir=src:../briar-core/src
+external.libs.dir=../briar-core/libs
+
 # You can also use it define how the release builds are signed by declaring
 # the following properties:
 #  'key.store' for the location of your keystore and

briar-android/custom_rules.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<project name="Briar" default="help">
+<target name="-pre-compile">
+    <path id="project.all.jars.path">
+        <path path="${toString:project.all.jars.path}"/>
+        <fileset dir="${jar.libs.dir}">
+            <include name="*.jar"/>
+        </fileset>
+        <fileset dir="${external.libs.dir}">
+            <include name="*.jar"/>
+        </fileset>
+    </path>
+</target>
+</project>