Fix Issue #8298, Don't throw exceptions on broken symlinks.

Using dirEntries to loop trough all the files/directories in a directory
will curently throw an Exception when encountering an broken symlink.

Whit this change DirEntry will no longer throw an Exception for broken
symlinks, but in that case isDir and isFile will return flase while
isSymlink returns true.
fix Issue 11403 - functions in std.algo can't be used as pred
Make std.container.Array assert.
Remove dubious support for Unqual!R
Tweak blocks for consistency
Make internal attributes private
Tweak save implementation
tweak opDollar's DollarToken
new-style aliases
Use preconditions over asserts
rework slicing
Rework qualifiers in Cycle!Array
[trivial] remvoe trailing whitespace
std.file: Fix race condition when mkdirRecurse runs concurrently

mkdirRecurse would crash if a directory was created between its
exists() and mkdir() calls. This could occur if mkdirRecurse was called
at the same time from mutiple threads or processes.

Instead of relying on the exists() check to indicate whether the next
mkdir() should succeed, we explicitly ignore "already exists" errors
from the OS. Note that this changes the behavior of mkdirRecurse when
the leaf directory already existed: previously it would throw, whereas
now it will silently succeed. The new behavior is conformant with some
other implementations of "recursive mkdir": the -p flag of the GNU
tool, Ruby's mkpath, Java's mkdirs, and Perl's make_path. (On the
other hand, the old behavior was equivalent to the behavior of
Python's makedirs).
fix issue 11808
adjust documentation to reflect new capabilities
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.