Fix bug 7648 comment in `std.stdio.File` and add bug section to `std.file.slurp`.

Issue URL: http://d.puremagic.com/issues/show_bug.cgi?id=7648
Fix Issue 12556 - Add persistent byLine
Make byLineCopy support mutable line copies
Fix caching byLineCopy.front (oops)
std.math: Check if dmd-style inline asm is available
Issue 10194. Variant does not call struct destructors.
Implemented elaborate copying support.
Sanitize Appender constraints a bit.
Clarify when to use byLineCopy vs byLine
Fix issue 3363: std.stream.readf segfaults with immutabel format strings
Fix Issue 13042 - std.net.curl.SMTP doesn't send emails with libcurl-7.34.0 or newer
Start getting tests passing on Android/x86
Mark unittests for std.stdio.File.error, detach and flush as safe
Mark std.stdio.lockingTextWriter.this as safe
Merge pull request #2320 from tom-tan/safe-stdio-lockingTextWriter

Mark std.stdio.lockingTextWriter.this as safe
Merge pull request #2319 from tom-tan/safe-unittest-for-stdio-File-error-File-detach-File-flush

Mark unittests for std.stdio.File.error, detach and flush as safe
fix Issue 13098 - std.path functions no longer works with DirEntry
Merge pull request #2324 from MartinNowak/fix13098

[REG2.066a] Issue 13098 - std.path functions no longer works with DirEntry
Fix issue #13100 - std.process.setCLOEXEC() throws

There are two cases in which the fcntl() calls may fail:

  1) the file descriptor is invalid, in which case errno == EBADF,
  2) they receive invalid arguments, in which case errno == EINVAL.

We just want to ignore the error in the former case, as evidenced by
the bug report, and the latter means that we have an error in
std.process, which is best handled by an assertion. (Note that it was
never possible to catch the exception anyway, since it was thrown in
the child process.)
Merge https://github.com/D-Programming-Language/phobos into issue-3363