string padding: cpad, fix lpad and rpad (use strwidth not length).

The cpad function center pads a string by making appropriate calls
to lpad and rpad. The lpad and rpad functions should have been
using the strwidth function to determine how many columns strings
take up, but before they were incorrectly using `length` instead.

base/string.jl

@@ -1216,10 +1216,10 @@ end
 
 ## miscellaneous string functions ##
 
-function lpad(s::String, n::Integer, p::String)
-    m = n - length(s)
+function lpad(s::String, n::Integer, p::String=" ")
+    m = n - strwidth(s)
     if m <= 0; return s; end
-    l = length(p)
+    l = strwidth(p)
     if l==1
         return bytestring(p^m * s)
     end
@@ -1228,10 +1228,10 @@ function lpad(s::String, n::Integer, p::String)
     bytestring(p^q*p[1:chr2ind(p,r)]*s)
 end
 
-function rpad(s::String, n::Integer, p::String)
-    m = n - length(s)
+function rpad(s::String, n::Integer, p::String=" ")
+    m = n - strwidth(s)
     if m <= 0; return s; end
-    l = length(p)
+    l = strwidth(p)
     if l==1
         return bytestring(s * p^m)
     end
@@ -1240,11 +1240,9 @@ function rpad(s::String, n::Integer, p::String)
     bytestring(s*p^q*p[1:chr2ind(p,r)])
 end
 
-lpad(s, n::Integer, p) = lpad(string(s), n, string(p))
-rpad(s, n::Integer, p) = rpad(string(s), n, string(p))
-
-lpad(s, n::Integer) = lpad(string(s), n, " ")
-rpad(s, n::Integer) = rpad(string(s), n, " ")
+lpad(s, n::Integer, p=" ") = lpad(string(s),n,string(p))
+rpad(s, n::Integer, p=" ") = rpad(string(s),n,string(p))
+cpad(s, n::Integer, p=" ") = rpad(lpad(s,div(n+strwidth(s),2),p),n,p)
 
 # splitter can be a Char, Vector{Char}, String, Regex, ...
 # any splitter that provides search(s::String, splitter)