Fix shared_mutex and future time jump tests

[austin-beer]

This PR is composed of two commits.

The first commit simply reverts pthread/shared_mutex.hpp and future.hpp back to the versions in develop, which reverts all of the changes we've made to these two files to date.

The second commit re-fixes the time jump issues by using the predicate versions of the wait functions, which is a simpler solution than the one we were using before and which works even with the changes we made to avoid losing notifications.

[austin-beer]

Here are the test results from this PR.

https://github.com/austin-beer/test-time-jumps/blob/master/linux_results_austin_no_monotonic.txt https://github.com/austin-beer/test-time-jumps/blob/master/linux_results_austin_yes_monotonic.txt https://github.com/austin-beer/test-time-jumps/blob/master/windows_results_austin_no_generic_shared.txt https://github.com/austin-beer/test-time-jumps/blob/master/windows_results_austin_yes_generic_shared.txt

The only fixable failures that still need to be fixed after this PR are in:

win32/basic_timed_mutex.hpp
win32/basic_recursive_mutex.hpp
win32/shared_mutex.hpp

[viboes]

Thanks a lot for almost fixing everything. There is some hope we could have this for boost-1.66.