DMTCP-2.6.0 released

Newer flags for configure:
* Rename --enable-debug to --enable-logging
* Add --enable-debug: "-Wall -g3 -O0" (for debugging DMTCP)

Newer flags for dmtcp_restart:
* Add --debug-restart-pause flag to dmtcp_restart

Bug fixes and enhancements:
* Fixes for glibc versions greater than or equal to 2.24
* Fix deadlock in system() wrapper when the child crashes
* Fix deadlock when a process is forked in the resume phase (issue #691)
* jsocket: Warn user if peer closes socket while draining (issue #701)
* Fix epoll1 test (initialize addrlen for accept()) (#705)
* Fix to correctly calculate Coordinator/Host IP:
Affects some distributed applications
* Allow restored stack to grow if needed.
* Fix bug in POSIX timer: race condition manifested in test/timer.c/Ubuntu-18.04
* Modified InfiniBand plugin for more robust support
(primarily of interest for MPI)
* The floating point environment (fegetenv()) is now restored on restart.
(Formerly, only the rounding mode (fegetround()) was restored.)
* The current resource limits (rlim_cur) for RLIMIT_NOFILE and RLIMIT_STACK
are restored if possible.
* Mutex ownership and robust mutexes are now supported if DMTCP is configured
with --enable-mutex-wrappers. (However, this configuration can also add runtime overhead
if mutex operations are called very frequently.)
[Thanks to Johannes Stoelp, Laurent Buchard, Pankaj Mehta of Synopsys, Inc.]
* Fix bug if stack grows a lot after a restart.
* Improved support for pty's
* util/gdbinit-example added for those who wish to debug DMTCP internals.
* Many bug fixes