Make BigInt nothrow where possible
more operators nothrow
fix import declarations
Merge pull request #2211 from 9rnsr/fix12359

fix import declarations
Mark std.stdio.File.seek as @trusted
Merge pull request #2214 from tom-tan/trusted-stdio-File-seek

Mark std.stdio.File.seek as @trusted
Merge pull request #2210 from dymk/bignum-nothrow

Make BigInt nothrow where possible