[Fix #506] Makes display version command return the actual version (2)

[carlosgeos]

My previous PR (#507), only partially solves the problem (#506)

The byte-compiled file will look for the version in its headers but it has none.

The version has to be given to the byte compiled file at compile time (therefore using eval-when-compile).

Difference in the .elc files:
This PR:

master branch:

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And a small change: (lm-version) takes an argument, the file. This is cleaner than creating a temp buffer, inserting the contents of the current file and calling (lm-version) within this context.

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[bbatsov]

The commit message doesn’t seem right. I guess you can use a variation of your PR description instead.