Fix reading library name from .fd file

[tehKaiN]

Related to bebbo/amiga-gcc#214

Currently, the library filename is taken from two sources:

• if .fd file name is xxx_lib.fd, use xxx as library name
• otherwise, extract library name from librarybase variable defined inside .fd file

This wasn't warking for http://aminet.net/package/util/libs/Identify because it resulted in trying to load "Identify.library" instead of "identify.library". Amiga's OpenLibrary() opens the file and does the case-sensitive strcmp of the library name coded inside the file.

New code works similarly to the old version:

• if .fd file name is xxx_lib.fd, use xxx as library name
• otherwise, assume that the library name is same as full .fd file name

This probably also fixes CyberGraphics pack - it will try to open cybergraphics.library instead of CyberGfx.library.