Include import name in import shadowing error messages.

This partially alleviates the confusing behavior in issue #16597
Update compile-fail tests due to changed diagnostics
Add compile-fail test for missing import shadowing case
Register new snapshots
test: Ignore a deadlocking test on OSX

This test apparently keeps making no progress and timing out builds on the OSX
builder, so this commit is switching the test to be ignored.

cc #16872
auto merge of #16598 : bkoropoff/rust/import-shadow-name, r=alexcrichton

This partially alleviates the confusing behavior in issue #16597
auto merge of #16859 : alexcrichton/rust/snapshots, r=huonw
auto merge of #16873 : alexcrichton/rust/ignore-deadlocks, r=sfackler

This test apparently keeps making no progress and timing out builds on the OSX
builder, so this commit is switching the test to be ignored.

cc #16872
Center alignment for fmt

Use '^' to specify center alignment in format strings.

fmt!( "[{:^5s}]", "Hi" ) -> "[ Hi  ]"
fmt!( "[{:^5s}]", "H" )  -> "[  H  ]"
fmt!( "[{:^5d}]", 1i )   -> "[  1  ]"
fmt!( "[{:^5d}]", -1i )  -> "[ -1  ]"
fmt!( "[{:^6d}]", 1i )   -> "[  1   ]"
fmt!( "[{:^6d}]", -1i )  -> "[  -1  ]"

If the padding is odd then the padding on the right will be one
character longer than the padding on the left.