Add a Python test that values starting with the LSM tombstone can be inserted and retrieved.

refs #1032
We only append one byte to LSM values that start with the tombstone.

This fixes a bug that caused undefined behavior for applications inserting values into an LSM tree that begin with '\x14\x14'.

refs #1032.
Fix allocation for concatenation of wtperf command-line arguments.

Found when testing #1032 with `valgrind wtperf ... -C buffer_alignment=0`.