Akhil,

tried right now. didn't go well. 

I've substituted on point_of_sale.py (one of the first lines) the string

from openerp import tools 

with the new

from openerp import models, fields, api, exceptions, tools 

Then I've added the new inherit at the very end

class pos_order_line(models.Model):
   _inherit = 'pos.order.line'
    pos_categ = fields.Many2one(related='product_id.pos_categ_id', string="POS Category")

Sadly, I've got the following errors:

2015-05-07 22:02:21,150 2150 ERROR Divina_DB1 werkzeug: Error on request:
Traceback (most recent call last):
  File "/home/effe/.local/lib/python2.7/site-packages/werkzeug/serving.py", line 177, in run_wsgi
    execute(self.server.app)
  File "/home/effe/.local/lib/python2.7/site-packages/werkzeug/serving.py", line 165, in execute
    application_iter = app(environ, start_response)
  File "/home/effe/odoo/openerp/service/server.py", line 281, in app
    return self.app(e, s)
  File "/home/effe/odoo/openerp/service/wsgi_server.py", line 216, in application
    return application_unproxied(environ, start_response)
  File "/home/effe/odoo/openerp/service/wsgi_server.py", line 202, in application_unproxied
    result = handler(environ, start_response)
  File "/home/effe/odoo/openerp/http.py", line 1280, in __call__
    return self.dispatch(environ, start_response)
  File "/home/effe/odoo/openerp/http.py", line 1412, in dispatch
    ir_http = request.registry['ir.http']
  File "/home/effe/odoo/openerp/http.py", line 339, in registry
    return openerp.modules.registry.RegistryManager.get(self.db) if self.db else None
  File "/home/effe/odoo/openerp/modules/registry.py", line 353, in get
    update_module)
  File "/home/effe/odoo/openerp/modules/registry.py", line 384, in new
    openerp.modules.load_modules(registry._db, force_demo, status, update_module)
  File "/home/effe/odoo/openerp/modules/loading.py", line 351, in load_modules
    force, status, report, loaded_modules, update_module)
  File "/home/effe/odoo/openerp/modules/loading.py", line 255, in load_marked_modules
    loaded, processed = load_module_graph(cr, graph, progressdict, report=report, skip_modules=loaded_modules, perform_checks=perform_checks)
  File "/home/effe/odoo/openerp/modules/loading.py", line 143, in load_module_graph
    load_openerp_module(package.name)
  File "/home/effe/odoo/openerp/modules/module.py", line 315, in load_openerp_module
    __import__('openerp.addons.' + module_name)
  File "/home/effe/odoo/openerp/modules/module.py", line 80, in load_module
    mod = imp.load_module('openerp.addons.' + module_part, f, path, descr)
  File "/home/effe/odoo/addons/point_of_sale/__init__.py", line 24, in <module>
    import point_of_sale
File "/home/effe/odoo/addons/point_of_sale/point_of_sale.py", line 1467
    pos_categ = fields.Many2one(related='product_id.pos_categ_id', string="POS Category")
 IndentationError: unexpected indent

Back to square one... 

SOLVED WITH:

class pos_order_line (osv.Model):
    _inherit = 'pos.order.line'
    _columns = {
        'product_categ_name': fields.related('product_id', 'categ_id', 'name', type='char', string='Product Category', store=True, readonly=True),
}