Revision of help pages for mesh function (en_US, pt_BR).

Change-Id: I799f5922b085fa90d2c83a0e2c6865594e2cfac0
Translation of help page for mesh function into Russian.

Change-Id: Ibb19c08d2a68e89bce2fba0c1b497cf49c567492
Insert a latex instruction in xtitle (on help pages for mesh function).

The latex instruction gives better presentation of mathematical expression.
The instruction \huge gives the size of symbols which looks good on the figure.

Change-Id: Ibe927bd1f2edc58a7b4eda9e6c76fb120642068c
Revision of help pages for atand function.

Inserted the link to atan function.

Change-Id: I0b48f6b79a8a4464b478d995b1b937f34671fd39
Xcos c_pass2: improve the show_comment display

Change-Id: If575593a08f975df2721aedb2c6083257960bcd4