rm(force=true) clobbers exception

[maleadt]

MWE:

main() = error("test")

try
    main()
catch ex
    rm("nonexisting"; force=true)
    rethrow(ex)
end

This reports a stacktrace pointing to the failed uv_error (because of nonexisting not existing), which should have been caught and discarded, and not to our ErrorException:

Stacktrace:
 [1] uv_error at ./libuv.jl:68 [inlined]
 [2] unlink(::String) at ./file.jl:500
 [3] #rm#7(::Bool, ::Bool, ::Function, ::String) at ./file.jl:145
 [4] (::Base.Filesystem.#kw##rm)(::Array{Any,1}, ::Base.Filesystem.#rm, ::String) at ./<missing>:0
 [5] include_from_node1(::String) at ./loading.jl:569
 [6] include(::String) at ./sysimg.jl:14
 [7] process_options(::Base.JLOptions) at ./client.jl:305
 [8] _start() at ./client.jl:371

Printing ex after the call to rm still reports the ErrorException, so I guess the nested try ... catch to implement rm's force mode clobbers whatever global state contains the current active exception.

Tested on 0.5, 0.6 and master.

[yuyichao]

Dup of #19979 and related to #13947