Memory lines may contain address symbol

Previously I didn't handle GDB eXamine output which contained symbol
for addresses like the following:
0x100000d0 <impure_data>:	0x00000000	0x00005fb8	0x00005fd8	0x00005ff8

I updated isMemoryLine() to check for 0xXXXXXXXX instead of just
looking at the first two characters (0x) and a trailing ':'.