Merge branch 'jk/fix-alias-pager-config-key-warnings' into maint

Because the configuration system does not allow "alias.0foo" and
"pager.0foo" as the configuration key, the user cannot use '0foo'
as a custom command name anyway, but "git 0foo" tried to look these
keys up and emitted useless warnings before saying '0foo is not a
git command'.  These warning messages have been squelched.

* jk/fix-alias-pager-config-key-warnings:
config: silence warnings for command names with invalid keys

diff --cc cache.h
Simple merge

diff --cc config.c
Simple merge

diff --cc pager.c
Simple merge

diff --cc t/t7006-pager.sh
Simple merge