redis-stat unable to build on Ubuntu 12.04 64-bit

Had an issue where it could not be built:

```
cc -o redis-stat -std=c99 -pedantic -O2 -Wall -W -lm -pthread -g -rdynamic -ggdb redis-stat.o zmalloc.o utils.o deps/hiredis/libhiredis.a
redis-stat.o: In function `samplesToGraph':
/root/redis-tools/redis-stat.c:460: undefined reference to `pow'
```

The problem is the `-lm` flag needs to move to the end of the line, due to the way `gcc` loads things. If the make line is switched to the following, it works fine:

```
cc -o redis-stat -std=c99 -pedantic -O2 -Wall -W -pthread -g -rdynamic -ggdb redis-stat.o zmalloc.o utils.o deps/hiredis/libhiredis.a -lm
```

I am not the best with C compilation, so I am unsure if this is an OS specific issue, or applies to GCC in general.

System Info:
GCC: `gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3`
Uname: `Linux redis 3.2.0-31-virtual #50-Ubuntu SMP Fri Sep 7 16:36:36 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux`
Git Hash of Repo: `0f46ef40e6f178464c4c7bc3070c24ad5b5e0ec8`