Make a confusing error message clearer.

# Check for the current jdk

ifeq ($(requires_openjdk), true)

# The user asked for java7 openjdk, so check that the host

# java version is really openjdk

# The user asked for openjdk, so check that the host

# java version is really openjdk and not some other JDK.

ifeq ($(shell echo '$(java_version_str)' | grep -i openjdk),)

$(info ************************************************************)

$(info You asked for an OpenJDK 7 build but your version is)

$(info You asked for an OpenJDK based build but your version is)

$(info $(java_version_str).)

$(info ************************************************************)

$(error stop)