The Himalayan kingdom of Nepal was set for historic change Wednesday with an assembly expected to abolish the country's 240-year-old monarchy, in a key victory for former Maoist rebels.  Security was tight around the venue for the assembly, which is set to dissolve the monarchy and sack the unpopular King Gyanendra when it holds its first session Wednesday.  Scores of police ringed the conference centre in Kathmandu after a series of bomb blasts in the runup to the meet by suspected "anti-republicans" supporting Gyanendra, who ascended the throne seven years ago after a palace massacre.  A homemade bomb exploded in a Kathmandu park on Tuesday shortly after Constituent Assembly members were sworn in, injuring two people.