Configure: improved layout of the generated makefile.

No functional changes.
Configure: improved make dependencies for perl module.

Added missing dependencies for perl module's Makefile.

Simplified dependencies for perl module nginx.so: it depends
on Makefile that in turn depends on other perl bits.
Configure: fixed perl module make rules.

Filename extension used for dynamically loaded perl modules isn't
necessarily ".so" (e.g., it's ".bundle" on Mac OS X).

This fixes "make" after "make" unnecessarily rebuilding perl module.
Simplified nginx version maintenance.

It's no longer necessary to update src/http/modules/perl/nginx.pm
when version is bumped, as it's now derived from src/core/nginx.h.
Configure: unified nginx version computation constructs.