ACCUMULO-1973 Add a warning if we don't find non-default values for namenode configuration

This is one of biggest confusions that new users seem to run into when
trying to initialize Accumulo (as it's a problem with us not finding
Hadoop configurations). Hadoop will work properly, as its configuration
is likely correct, but Accumulo can't find core-site.xml, tries to write
to the root of the local fs, and fails. Try to be a bit more explicit
about what happened when we initialized and the Configuration from the FS.
Merge branch '1.4.5-SNAPSHOT' into 1.5.1-SNAPSHOT
Merge branch '1.5.1-SNAPSHOT' into 1.6.0-SNAPSHOT
ACCUMULO-2127 Add note to append hadoop2 classpath entries in example configs
Merge branch '1.4.5-SNAPSHOT' into 1.5.1-SNAPSHOT

Conflicts:
	conf/examples/2GB/standalone/accumulo-site.xml

Also update the vfs-classloader general.classpaths example to match the rest of the examples
Merge branch '1.5.1-SNAPSHOT' into 1.6.0-SNAPSHOT

Conflicts:
	conf/examples/1GB/native-standalone/accumulo-site.xml
	conf/examples/1GB/standalone/accumulo-site.xml
	conf/examples/2GB/native-standalone/accumulo-site.xml
	conf/examples/2GB/standalone/accumulo-site.xml
	conf/examples/3GB/native-standalone/accumulo-site.xml
	conf/examples/3GB/standalone/accumulo-site.xml
	conf/examples/512MB/native-standalone/accumulo-site.xml
	conf/examples/512MB/standalone/accumulo-site.xml
	conf/examples/vfs-classloader/accumulo-site.xml