Column totals block customization issues

Recently I was trying to create custom block to display totals under one of the columns in grid I was working on.

Here are several problems I'm came across trying to do that:

• attempt to define block and give it's name in "total_block" in column definition failed (code doesn't even look there)
• I somehow managed to get it working, but I asked me to place "'" (single quotes) around inside my block, plus placing "," after that all.

I've managed to fix that inconsistencies and here is the patch.

To Test:

1. Add totals_render_as="grid_total_row" parameter to "grid" block rendering
2. Add totals="SUM" on any reasonable field
3. Add total_block="grid_custom_total_td" to that field definition in grid

Now you must see that custom block content as total under your column. If custom block isn't defined, then default block must be shown (verify that too).

Same override problem issue with column header block (that one with sorting arrow). Combined patch attached for both issues.