Merge pull request #453 from laiwei/master

bugfix: memory leak and dir-creating not work
Use automake based checks ("make check") and use the mechanism for travis
Valgrind support for the test suite. valgrind gets used when called as "make check TESTS_STYLE=valgrind"
Use valgrind via travis
try to get travis to run the test suite....
install valgrind - needed for test suite
Currently, tests have to run in the CET timezone.
Valgrind changes for travis - show log and include supressions
name individual tests in Makefile.am
if a test fails report original exit code instead of just 1
Try to handle freeing of mmapped and malloced rrd_t objects transparently

This IS rather hackish - an OO inspired approach might be better, but adding
knowledge about mmapped memory to the free path even allows mixed
mmapped/malloced objects
Never ever should a function free an object that was passed in. At least this
is my opinion.
Also get rid of a specialised rrd_free function and clean up exit paths of
functions.
Merge branch 'automake-based-checks' into memory-management
get rid of temporarily introduced fixed hash value
Make rrd_free idempotent by resetting free'd pointers to NULL
add RRD_READVALUES option to rrd_open
- in case of mmap just point to the correct position within the file
Use RRD_READVALUES to read data
Start modify/tune unification
Fix nasty double-free error in rrd_free (duh!)
Merge branch 'memory-management' into rrdmodify-master