Reformatted autoconf/automake template files

Moved enabling/disabling of features entirely into the autoconf script.
Use the standard --enable-* / --disable-* syntax for features, no
parsing required.  Cleaned up whitespace in Makefile.am to fit with
common practices.
Issue #20 - revised Java detection methodology

The original method of using ./configure --with-java[=javac] implies
that Java support always occurs and the caller only wants to specify
which javac implementation to use.  The preferred method is to control
enablement of the featuring using --enable-java and then separately
control any aspects of the implementation using --with-* as necessary.

So this commit makes this happen:

  --enable-java
      Enables support for the Java bindings, primarily through building
      the libopendnp3java library

Once Java support is enabled, we can now specify the path to jni.h
through four different means (choose your poison):

  JAVA_HOME="/path/to/jvm/main/tree"
      Specifies the top-level path for the Java VM files.  A typical
      default might be /usr/lib/jvm/java-7-oracle on an Ubuntu
      installation running the Oracle Java 7 VM.

  JAVAC="/path/to/jvm/bin/javac"
      Specifies the path to the javac executable located inside the Java
      VM tree.  A typical default might be
      /usr/lib/jvm/java-7-oracle/bin/javac.

  --with-javac=/path/to/jvm/bin/java
      Like specifying the JAVAC environment variable, but using an
      autoconf flag instead.

  --with-jni-include-path=/path/to/jvm/include
      Specifies the path directly to directory that contains the jni.h
      header.  A typical default might be
      /usr/lib/jvm/java-7-oracle/include.

A combination of the two sets is needed to properly enable support:

  # Assuming JAVA_HOME is set as part of your system's environment
  ./configure --enable-java

  # Overriding JAVA_HOME
  ./configure --enable-java JAVA_HOME="/usr/lib/jvm/java-7-oracle"

  # Using JAVAC and JAVA_HOME (indirectly)
  ./configure --enable-java JAVAC="${JAVA_HOME}/bin/javac"

  # Using --with-javac
  ./configure --enable-java --with-javac=${JAVA_HOME}/bin/javac

  # Using --with-jni-include-path
  ./configure --enable-java --with-jni-include-path=${JAVA_HOME}/include
Issue #19 - detect need for OPENDNP3_BOOST_TIMER_PATCH

If the Boost version is detected to be less than 1.50.0, autoconf now
adds -DOPENDNP3_BOOST_TIMER_PATCH to CPPFLAGS.