find_end randomly fails with SIGABRT on Travis CI

[jszuppe]

I don't know why, but find_end algorithm sometimes fails with with SIGABRT in find_end_string test case. It happens rarely and only with AMD APP SDK (both 2.9.1 and 3.0) on Travis CI (I have an Intel CPU like Travis CI and I wasn't able to reproduce on my PC.) and only on the second ctest --output-on-failure run. I might be AMD APP SDK issue. I'll investigate it.

32/165 Test  #32: algorithm.find_end ...................***Failed    0.17 sec
test_find_end: /home/travis/build/haahh/compute/test/test_find_end.cpp:60: void compute_test::find_end_string::test_method(): Assertion `iter == vectort.begin() + 15' failed.
Running 2 test cases...
unknown location(0): fatal error in "find_end_string": signal: SIGABRT (application abort requested)

Examples:

• https://travis-ci.org/boostorg/compute/jobs/112436799 (develop)
• https://travis-ci.org/haahh/compute/jobs/112264011#L7337

[jszuppe]

Fixed by #597.