FT-594 add fractal tree version 24 (tokudb 7.0.1) and version 27 (tokudb 7.5.0) stress data directories
FT-594 add fractal tree version 26 stress data directories
FT-596 Fix a variety of drd failures by wrapping access to benign racy
variables with `drd ignore var' and `drd stop ignoring var'
Merge branch 'releases/tokumx-2.0'
FT-599 switched from _SVID_SOURCE to _DEFAULT_SOURCE

Newer libc doesn't like _SVID_SOURCE:
https://sourceware.org/ml/libc-alpha/2013-12/msg00652.html
Merge branch 'bugs/599'
FT-600 locktree refs crash test and bug fix
fixed cmake warnings for 3.0.0
disabled keyrange until we fix it
optimized test_keylen_diff so it's faster under valgrind

also widened one valgrind suppression to also catch something we
initialize in the assert layer
fixed some helgrind warnings in ydb/helgrind_test_groupcommit_count.tdb
moved to generator expressions for cmake debug flags
use TOKU_ macros to handle !USE_VALGRIND
fixed some valgrind sanity tests
fixed cmake policy CMP0022:

either use all-plain or all-keyword style of target_link_libraries
Merge branch 'ft600'
Merge branch 'ft600' into releases/tokudb-7.5
fixed cmake for versions without generator expressions (hopefully)
fixed version check inequality
Merge commit '1e3bc86b0901c0005551442b89d3a8d392b2ce6d' into releases/tokudb-7.5