Closes Homebrew/homebrew#27 (permissions to strict)

I went with 0555 as the permissions changing only occurs to bin, sbin and lib, so there shouldn't be any files in there for editing in general anyway.

Formulae can specify not to "clean" any particular file by reimplementing the skip_clean? function, in case some config file or what not ends up in there.

Also committing cosmetic fix to pretty_duration function.

Library/Homebrew/brew.h.rb

@@ -260,7 +260,7 @@ private
       `strip #{args} #{path}`
     else
       # strip unlinks the file and recreates it, thus breaking hard links!
-      # is this expected behaviour? patch does it too… still,mktm this fixes it
+      # is this expected behaviour? patch does it too… still, this fixes it
       tmp=`mktemp -t #{path.basename}`.strip
       `strip #{args} -o #{tmp} #{path}`
       `cat #{tmp} > #{path}`
@@ -271,13 +271,13 @@ private
   def clean_file path
     perms=0444
     case `file -h #{path}`
-      when /Mach-O dynamically linked shared library/
-        strip path, '-SxX'
-      when /Mach-O [^ ]* ?executable/
-        strip path
-        perms=0544
-      when /script text executable/
-        perms=0544
+    when /Mach-O dynamically linked shared library/
+      strip path, '-SxX'
+    when /Mach-O [^ ]* ?executable/
+      strip path
+      perms=0555
+    when /script text executable/
+      perms=0555
     end
     path.chmod perms
   end

Library/Homebrew/utils.rb

@@ -42,9 +42,9 @@ def onoe error
 end
 
 def pretty_duration s
-  return "#{(s*1000).to_i} milliseconds" if s < 3
-  return "#{s.to_i} seconds" if s < 10*60
-  return "#{(s/60).to_i} minutes"
+  return "2 seconds" if s < 3 # avoids the plural problem ;)
+  return "#{s.to_i} seconds" if s < 120
+  return "%.1f minutes" % (s/60)
 end
 
 def interactive_shell