make gcdx type-stable & 20x faster, fix invmod to work with negative arguments, use GMP for BigInt invmod
make gcd and lcm positive (fix #4810)
update gcd/lcm/gcdx docs
ensure consistent results for gcdx(0,0) with BigInt
bugfix for lcm(0,0), add test coverage of gcd-related functions
fix powermod problems, add test coverage
update NEWS for gcd fixes
simplify checks in powermod, and add more tests
improved error messages, removed commas and function names in error text
error text formatting back to all red
Merge branch 'errors' of https://github.com/davidssmith/julia into errors
errors