Merge pull request #28 from concretevitamin/master

Use inherits() to test an object's class.
Update README with maven proxy instructions
Add tests for partition with string keys
Add two tests one with a string array and one from a textFile to test
both codepaths
Merge branch 'master' of github.com:amplab/SparkR-pkg into string-tests

Conflicts:
	pkg/inst/tests/test_textFile.R
Fix bug where serialized was not changed for RRRD
Reason: When an RRDD is created in getJRDD we have converted any
possibly unserialized RDD to a serialized RDD.
Merge pull request #30 from shivaram/string-tests

Add tests for partitioning with string keys
22x speed improvement, 3X mem impovement

data = apply(matrix(as.character(1:90000), ncol= 300), 1, paste, collapse = " ")
system.time(readPartition(data))
system.time(readPartition.old(data))
faster parsing
replace require with library

require is used only when there is a way to recover from a failure to
load a package. Since these examples would all fail if any of the
missing libraries were required, using require only delays the error
and makes it less clear.
implemented using matrices and vectorized calls wherever possible
for rstudio users
vectorized version, 36s 10 slices 10^6 per slice. The older version takes 30 sec on 1/10th of data.
Exclude protobuf from Spark dependency in Maven
This avoids pulling in multiple versions of protobuf from
Mesos and Hadoop.
Merge pull request #34 from shivaram/master

Exclude protobuf from Spark dependency in Maven
Cache sbt, maven, ivy dependencies
on_failure -> after_failure in travis.yml
Merge pull request #35 from shivaram/master

Cache sbt dependencies in travis.yml
converted tabs to spaces per project request
more formatting per committer request
and more formatting