Broadcast over constants in multiply!() and add!()

Permit the arguments to multiply! and add! (and by extension,
divide! and the copying versions) to be arrays, and broadcast
over them.  This allows for example

    julia> multiply!(s, s[:depmax])

to normalise the traces in `s` by their maximum positive amplitude.

src/SAC.jl

@@ -889,7 +889,7 @@ envelope!(s::SACtr) = envelope!([s])
 Multiply the values in a SAC trace by `value`
 """ ->
 function multiply!(a::Array{SACtr}, val)
-    for s in a s.t[:] = s.t[:]*val end
+    for s in a s.t[:] = s.t[:].*val end
     update_headers!(a)
 end
 multiply!(s::SACtr, val) = multiply!([s], val)
@@ -901,7 +901,7 @@ mul! = multiply!
 Add a constant value to a SAC trace
 """ ->
 function add!(a::Array{SACtr}, val)
-    for s in a s.t[:] = s.t[:] + val end
+    for s in a s.t[:] = s.t[:] .+ val end
     update_headers!(a)
 end
 add!(s::SACtr, val) = add!([s], val)