Fixed typos with the variable name op1 and op2.

There is also a typo that I could not fix because I'm lazy:

def i_LDRD(i,fmap):
    cond,dest,src,sht = __pre(i,fmap)
    off_addr = (src+sht) if i.add else (src-sht)
    adr = off_addr if i.index else src
    res1 = fmap(mem(adr,32))
    res2 = fmap(mem(adr+4,32))
    fmap[dst1] = tst(cond,res1,fmap(dst1))
    fmap[dst2] = tst(cond,res2,fmap(dst2))
    if i.wback:
        fmap[src] = tst(cond,fmap(off_addr),fmap(src))

dst1 and dst2 do not exist.
Fixed the indentation of the script.
Now InstructionError works and shows the instruction at fault.
Fixed indentation issues and typos.