std.file: Simplify/optimize mkdirRecurse

The left.length != pathname.length check both takes care of the
Windows-only check, and it avoids a pointless stat on the FS root.
Merge pull request #1835 from monarchdodra/cycle2

Bring the noise to Cycle
Merge pull request #1818 from CyberShadow/std-file-mkdirRecurse

std.file: Fix race condition when mkdirRecurse runs concurrently
Merge pull request #1713 from monarchdodra/ArrayAssert3

Make std.container.Array assert.
fix issue 11839
Merge pull request #1819 from monarchdodra/equalEqual

fix Issue 11403 - functions in std.algo can't be used as pred
Fixup commit a8177b8cc3300fd64eef0acb7397be15fb0e0b4c

Per https://github.com/D-Programming-Language/phobos/commit/a8177b8cc3300fd64eef0acb7397be15fb0e0b4c#commitcomment-4991972 :
"nothrow" was superfluous
Merge pull request #1839 from monarchdodra/cycle3

Fixup commit a8177b8cc3300fd64eef0acb7397be15fb0e0b4c
add _ to allowed characters in regex identifier
fix issue 11350

Do not throw on bad UTF inside of a C callback
fix issue 8203, similar issue with lookaround

When using a temporary engine as closure its generation counter
should be tracked separately for each lookaround.

For now just use built-in AA, later we could find better places
to store this counter in.
Merge pull request #1841 from blackwhale/issue-8203

fix issue 8203, similar issue with lookaround
Merge pull request #1838 from blackwhale/issue-11839

Fix issue 11839
Merge pull request #1837 from blackwhale/issue-11808

Fix issue 11808 std.uni.CodepointSet('А', 'Я'+1, 'а', 'я'+1) asserts
Merge pull request #1142 from MikeWey/Issue8298

Fix Issue #8298, Don't throw exceptions on broken symlinks.
Merge pull request #1842 from blackwhale/issue-11350

Fix issue 11350 ibphobos2 regex match segfaults when a rare HTTP header is received
Remove trailing white
Remove tabs
Fix issue 11884 - std.container.Array lacks a constructor from an input range
Merge pull request #1844 from monarchdodra/fix11884

Fix issue 11884 - std.container.Array lacks a constructor from an input ...