Add more functions to qmake

Add the following new functions to 'qmake':

• runique( list_variable ):

Removes words duplication in the provided list. It works like
unique function with only one difference. It starts looking from the
last element and removes duplications till list's head.

• convert_separators( path )

Returns a path with the '/' separators converted to separators
that are appropriate for the underlying operating system.

• eval( variable )

Evaluates variable's value by replacing all references to
variables and performing replacement functions.

• eval_cap( variable )

Works like eval command but replace all output letters capital.

• exit( messageText )

Aborts project file's processing and print messageText to output
console.

• direxists

description is almost the same like "exists" has, but it works
with a directory. See "exists".

• tofile( filename, message )

"Message" text string will be appended to "filename" file