Log Message:

Now the package os done
pkg_src_update_summary incrementally updates summary about all
packages in pkgsrc source tree.

Algorithm. 1) pkg_src_update_summary quickly obtains micro summary
information about all packages from pkgsrc source tree, "micro" means
PKGNAME and PKGPATH fields only.  2) comparing summary_filename and
micro summary collected in step 1 by PKGNAME field.  3) copying
summary from summary_filename about unchanged packages.  4) collecting
full summary information about all changed and new packages.  5) new
summary = 3+4