Added a source attribute to the javac task to silence one build warning....

... (source is same as target version, i.e. java 1.5)

With the original build file, which lacks a "source" attribute on the javac task, we get this warning in the output:

compile:
    [javac] /home/rbouman/eclipse-workspace/cmme-editor/build.xml:20: warning: 'includeantruntime' was not set, defaulting to build.sysclasspath=last; set to false for repeatable builds
    [javac] Compiling 2 source files to /home/rbouman/eclipse-workspace/cmme-editor/build
    [javac] 
    [javac]           WARNING
    [javac] 
    [javac] The -source switch defaults to 1.7 in JDK 1.7.
    [javac] If you specify -target 1.5 you now must also specify -source 1.5.
    [javac] Ant will implicitly add -source 1.5 for you.  Please change your build file.
    [javac] warning: [options] bootstrap class path not set in conjunction with -source 1.5
    [javac] 1 warning

This pull request implements the advice given in the warning output. After this change, only the "warning: [options] bootstrap class path not set in conjunction with -source 1.5" remains.