REF: ensure O(N log N) when using fft for acf

The numpy implementation will fall back to a O(N**2) version of the fft
in cases where it cannot factorize the array length, which can be a
increase in runtime of several order of magnitude. This uses the
_next_regular function from scipy to ensure that we always use array
lengths for which fftpack is optimized.
TST: add test for _next_regular

also copy the test for _next_regular from scipy
TST: Adjust precision
TST: Add self to method args
REF: Avoid setting a copy warnings from pandas
BUG: Fix no longer works pandas assignment. Closes #1377.
BUG: Pass kwargs along to plot
REF: try using less memory in multipletests 'holms' see #1394
REF: reduce memory in fdrcorrection (minimal change)
REF: allow is_sorted in fdrcorrection see #1394
REF: add is_sorted option to fdr to avoid duplicate calculations
     delete intermediate arrays (all work except Hommel)
REF: multipletests: add is_sorted, performance: drop reverse indexing
     docstring
TST: multipletests: add tests for is_sorted
REF/DOC: use take (a bit faster), timing in docstring
Merge pull request #1396 from josef-pkt/multitest_memory

REF: Multipletests reduce memory usage
TST: genmod test_link, change precision to allclose
STY/TST: families test_link, convert tests to test_function
Merge pull request #1404 from josef-pkt/TST_fix_genmod_link_tests

TST fix genmod link tests
MAINT: Fix path.
MAINT: E-mail the whole traceback.