inconsistency in output during installation

[ignatenkobrain]

Installing src/cpp/libxmlrpc_client++.so.8.47 to /home/brain/tmp//usr/local/lib64/libxmlrpc_client++.so.8.47
Installing openssl_thread.h to /home/brain/tmp//usr/local/include/xmlrpc-c
Installing /home/brain/git/upstream/xmlrpc-c/tools/xml-rpc-api2cpp/xml-rpc-api2cpp.1 to /home/brain/tmp//usr/local/share/man/man1.

There are 3 kind of outputs:

1. Installation by keyword from library(), perfectly fine, shows subdir and location where is installing
2. Installation by install_headers(), missing subdir and destination filename
3. Installation by install_man()/install_data()/pkgconfig.generate(..., install:true), shows full path, doesn't show destination filename and fullstop at the end

[nirbheek]

Related: #3006