fixing problems when importing from blogger

this was done in 3 commits at https://github.com/ccanepa/nikola/tree/blogger6.0.2

 	fix crash when importing to an existing site due to strftime bad format
  	fix import_blogger crash due to missing symbols for template 
	fix import_blogger warning (URL not ending in /) at build time

as of today, 2013 09 13 , it worked with my blogger dump, no warnings, resulting site looks good with nikola serve