mnc: provide MUNIN_MASTER_IP
fix autotools usage

 * Add Makefile.am to each subproject, so make can be invoked from
   subdirs
 * Do not pass unneeded -DPLUGINDIR to munin-plugins-c
 * Fix "fails to make twice in a row". The all-local target used wrong
   link test
 * The binaries are now located in subproject directories. Adapt paths
   in .gitignore and elsewhere.
Merge remote branch 'helmut/fix-autotools-usage'
gitignore output exe