revert version number of mpfr to 3.0.1

... and debug the problem later
fix a syntax error
fix message about elapsed time
set the free space divisor of libgc when running examples
add some debug and assert flags in debug mode
Merge pull request #153 from jakobkroeker/dan.master.add.assertion.flags.in.debug.mode

add some debug and assert flags in debug mode
revert enable-debug in factory
Merge pull request #154 from jakobkroeker/dan.master.add.assertion.flags.in.debug.mode

revert enable-debug for factory
my makefile
revert changes involving libgc tuning parameters

... GC_FREE_SPACE_DIVISOR and GC_INITIAL_HEAP_SIZE, because our examples and
tests are constrained by limits on both memory and time, and if we speed up a
run by consuming more memory, some of the examples will exceed their limits.
Merge branch 'master' of https://github.com/Macaulay2/M2
disable tests for library atomic_ops
Merge remote-tracking branch 'upstream/master' into experimental
fix bug in failed in attempted improvement of minimalPrimes; put constant in front in factor