Revert "[XrdCl] Use the built-in poller ::Pause method when stopping and restarting the poller"

This reverts commit fd991cf34a65e8be66b8763c47fd636d3dd84273.
Revert "Extend Pause/Resume to all platforms and remove CPU burner when paused."

This reverts commit c52bc62c6c08d8acd43a3e4fe3d2900c8f124bb1.
Revert "Correct conflict between comments and the code."

This reverts commit d14382b4ae5f2a4ac081afbb18c625006ed39312.
Revert "Initialize implicitly referenced fields to keep Valgrind happy."

This reverts commit ce3315bc2a2247e68af5c795d057108b4d4d91f9.
Revert "Provide a poller pause/resume method to ease forking without spurious errors."

This reverts commit 1f47a789db1d84ad58e69efd2679ec92ce4c8c47.
[XrdCl] Fix coverity issues
[XrdCl] Fix a very rare segfault when forking under heavy load
Merge branch 'poller'