Improve LibraryMaker.exe e.g. Some more checks

[IceSoft]

The tool LibraryMaker should be a little bit user friendly.
e.g. Some more info if there something missed or wrong.

Reason:
After using LibraryMaker I get this error during compiling now:

C:\Program Files\PureBasic\Compilers>pbcompiler.exe test.pb

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PureBasic 4.61 Beta 1 (Windows - x86)
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Compiling test.pb
Loading external libraries...
Error: Duplicated library command: abc() (in libraries MyLib and MyLib).