formula, resource: output when verifying checksum.

References Homebrew/homebrew#24566.

Library/Homebrew/formula.rb

@@ -534,6 +534,7 @@ class Formula
 
   # For FormulaInstaller.
   def verify_download_integrity fn
+    ohai "Verifying #{fn.basename} checksum" if ARGV.verbose?
     active_spec.verify_download_integrity(fn)
   end
 

Library/Homebrew/resource.rb

@@ -84,6 +84,7 @@ class Resource
 
   def verify_download_integrity fn
     if fn.respond_to?(:file?) && fn.file?
+      ohai "Verifying #{fn.basename} checksum" if ARGV.verbose?
       fn.verify_checksum(checksum)
     end
   rescue ChecksumMissingError