std.mmfile: Improve error handling

Use wenforce instead of (inappropriately) errno.
Switch from if blocks to scope blocks.
std.mmfile: Fix Windows anonymous mapping creation to conform to MSDN
Add setProxyAuthentication() in std.net.curl
Make std.file.readLink safe
Make std.file.DirEntry._ensureStatDone safe
not with multiple arguments
Improve find's @safety
Fix unpredictableSeed so that rndstuff can be used in @safe code

Allows:
1) canFind's tests to be @safe
2) allows the remainder of find's tests to be @safe
map should be @safe
cycle should be @safe
equal should be @safe
sequence should be @safe
cmp should be @safe
minPos should be @safe
mismatch should be @safe
livenshteinDistance should be @safe
copy should be @safe
swapRanges and reverse should be @safe
bringToFront should be @safe
remove should be @safe