test: common.bash:__getCheckSum: Don't rely on IFS

I managed to stumble across a bug in BATS where the run() function
screwed with the global IFS.  The bug has been fixed in git, but isn't
in a release yet.

sstephenson/bats#89

Anyway, this bug breaks __getCheckSum().  Fortunately, we have avoided
tripping it so far because luck has it that we never call
__getCheckSum() after run() in the same test.

So, there's nothing actually broken here, but it makes me nervous.  So
go ahead and modify __getCheckSum to not rely on IFS.

And, while we're at it: declare the result variable and set it as
separate commands.  Doing both in the same command masks the exit code
of the subshell expansion.  We don't explicitly check the exit code,
but BATS runs the test suite with `set -e`, so splitting it does mean
that BATS will now detect errors from sha1sum.  We don't really expect
that to happen, but if BATS will give us error checking on it for
free, why not?

test/lib/common.bash

@@ -9,8 +9,9 @@ __updatePKGBUILD() {
 }
 
 __getCheckSum() {
-	local result=($(sha1sum $1))
-	echo ${result[0]}
+	local result
+	result="$(sha1sum "$1")"
+	echo "${result%% *}"
 }
 
 __buildPackage() {