check-recipe in batch mode, -Wno-features

Allow checking recipes in --batch mode. Add option to suppress warnings
about :features since there are so many recipes that trigger this.
check-recipe: report parse errors

also fix previous commit which caused recipe warnings to show up
in *Warnings* instead of *el-get check recipe*.
el-get-check-recipe-batch: set exit status
add more warning suppressions

remove redundant erase-buffer call
check recipes in travis, fix or muffle warnings

suppressed warnings: -Wno-features -Wno-github -Wno-autoloads, because
too many recipes trigger them to handle right now.
check-recipe-batch: recipes/*.rcp -> recipes/

The travis script has set -e enabled which prints out command line to be
executed. However, it prints the command line after glob expansion, so
having recipes/*.rcp in a command would be a pain to scroll through.