generalized and more efficient cat implementation
fix incorrect mod rounding
dSFMT: use fill_array_* API instead of genrand_* API

Both APIs are not very compatible, so let's use fill_array_* functions, which
are faster but require MersenneTwister to have an additional array field.
make Julia global RNG be an instance of MersenneTwister

The state of the global RNG was previously handled by libdSFMT.
This commit allows the global RNG to benefit speed improvements resulting
from the use of fill_array_* functions (cf. previous commit).

However, scalar calls to rand() (i.e. producing one value instead of
filling an array) using the global RNG are now slower, as well as those
filling non-Float64 arrays (less than twice as slow though).
documentation for #7704
Hopefully fix #8842, objconv dependency not right
slight reduction in the number of comparisons for quicksort
We needed to move the objconv rules to above the openblas rules

Fixes #8842
make min/max stable. fixes #8825
remove some unnecessary Char methods
fix #8851, type intersection bug in Grid.jl tests exposed by `call` overloading
dSFMT: remove _gv_* and _genrand_* methods

They became unneeded after 06fb0a32.
test case for #8825
added missing minmax(::Any,::Any)