Fix vector syntax in error messages
remove oldsmallintmap

Closes #4738
Fix slice printing
test: Fix comments in pretty-printed test. rs=burningtree
Report error for non constant vector repeat count

Fix issue #3645
test: xfail-pretty some benchmarks. rs=burningtree
etc: Add a suppression for more enum instruction scheduling botches. rs=burningtree
test: Residual de-muting of the test suite. rs=demuting
test: De-~mut the test suite. rs=demuting
Revert "test: De-~mut the test suite. rs=demuting"

This reverts commit f63efdc2100ff28e2a42600641835e7bd8bde591.
auto merge of #5095 : thestinger/rust/smallintmap, r=catamorphism

Closes #4738.

The `std::smallintmap` module doesn't use an implicit @ box so I just added that explicitly for now to make porting simple.
auto merge of #5072 : youknowone/rust/repeat_count, r=brson

Fix issue #3645
auto merge of #5084 : oncemoreification/rust/issue-4517, r=brson

Patch for #4517

This works for fixed vectors, but I am unclear how slices should be printed, simply '&[...]'  or...

e.i. How should regions be printed?