Fix Astyanax slice end boundary handling

The Astyanax becakend had an equals() call comparing StaticBuffer and
ByteBuffer.  Because the concrete types differed, this call
unconditionally returned false.  Fixed to compare objects of the same
concrete type.

This failing equals() check caused the end boundary in Astyanax
getSlice() calls to be erroneously included in the results when it
should have been excluded.
Fix Cassandra Thrift end boundary handling

This commit fixes essentially the same problem my previous Astyanax
commit fixed.  An equals() call was comparing an object of type
StaticBuffer to ByteBuffer and unconditionally failing, causing
getSlice() calls to erroneously return the slice end instead of
excluding it.
Add test to catch new type of mutateMany() error

During the migration from ByteBuffer to StaticBuffer and friends, I
missed a Map in CassandraThriftStoreManager#mutateMany() that for
which get() calls used StaticBuffer keys but put() calls used
ByteBuffer keys.  These two types never equals() one another, so get()
always returned null.  The resulting bug made mutateMany() write each
key provided in its argument in at most one column family.  If a key
appeared under multiple column families in mutateMany()'s argument,
then only one CF actually received writes on the key, and all
additions/deteletions under the key in question were ignored for the
remaining CFs.

This bug caused a failure in a tangentially related test that touched
the buggy code plus a lot of other code.  This test just exercises the
buggy code.

A fix for the mutateMany() bug comes in the next commit.
Fixing broken Map calls in Thrift mutateMany()

Calls to get() on this map received StaticBuffer, while calls to put()
received ByteBuffer.  These types never return true for equals(), so
get() always returned null.  This was a bug introduced during the
ByteBuffer to StaticBuffer & friends conversion.

For additional discussion about the bug's failure mode, see the log
for 6aa352dc29c3fb0fe0ca3c80be328de32f74b42f.