allow an ε in comparison of grid coordinates

This fixes a test failure on i386 with recent versions of GCC where the numbers looked identical, even when printed with increased precision or in binary (hexfloat) format, for the test-dgf-yasp-offset test:

InvalidStateException [checkEntityLifetimeForCodim:.../dune-grid-2.6.0/dune/grid/test/checkentitylifetime.hh:77]:
ERROR! inconsistent corner(0) coordinate for entity 27
  (0 0.30000000000000004 != 0 0.30000000000000004)
  (0x0p+0 0x1.3333333333334p-2 != 0x0p+0 0x1.3333333333334p-2)

But the test still failed as i386's x87 FPU uses a higher precision internally.

Reference: https://buildd.debian.org/status/fetch.php?pkg=dune-grid&arch=i386&ver=2.6.0-4&stamp=1570661057&raw=0

changed milestone to %DUNE 2.7.0

added bugfix label

enabled an automatic merge when the pipeline for eff46396 succeeds

merged

mentioned in commit dd5d30f7

mentioned in commit d54d41af

mentioned in merge request !357 (merged)

mentioned in commit f7983c01