Add unittests: compare BigUint(0) to 0UL

to prevent regression of bug 12234.
Fixup Repeat condition
Fix Issue 11698 - readf doesn't work with bool
Implementation simplification for std.conv.parse!bool
[ARM] Some FPUs do not support exception trapping, disable test
Issue 3882: Inhibit more DMD warnings
Make adjoin's example a DDoc'ed unittest
Make adjoin take by auto-ref
Fix issue 12183 : Avoid using floating point in std.algorithm.sort.

- Prevent valgrind from aborting (some x87 FP operation are not supported).
- Can be slower on machines that have a soft floating point ABI.
Merge pull request #1994 from monarchdodra/adjoinDoc

Maintenance in adjoin
Merge pull request #1946 from Geod24/make-valgrind-happy

Fix issue 12183 : Remove use of floating point in std.algorithm.quickSortImpl
Make std.stdio.File.error and flush @trusted
Mark std.exception.ErrnoException.this as @trusted
Add missing imports
Merge pull request #1999 from monarchdodra/rangeImport

Missing imports in range
Merge pull request #1998 from tom-tan/trusted-exception-ErrnoException-this

Mark std.exception.ErrnoException.this as @trusted
Tweak map's save

Not only does it avoid opAssign issues, but the final code is simpler anyways.
Remove unnecessary enforce
Add test-cases for Issue 12349
Merge pull request #1997 from tom-tan/trusted-std-stdio-File-error-flush

std.File.flush and error causes segfault after calling close