ProgressUnknown display garbled when counter gets more digits

[stevengj]

It seems like the ProgressUnknown display is sometimes broken when the number of digits in the counter increases.

For example:

using ProgressMeter
prog = ProgressUnknown("Working:")
while true
    ProgressMeter.next!(prog)
    rand(1:2*10^8) == 1 && break
end
ProgressMeter.finish!(prog)

outputs

Working: 263805411 me: 0 Time: 0:00:13

It doesn't always happen — e.g. running the code above a second time gives

Working: 93336116        Time: 0:00:04

which looks okay.

[MarcMush]

fixed by #274