Remove some dead code

Based on coverity report.
execute: convert secure bits into mask properly

C.f. http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=5975c725dfd6f7d36f493ab1453fbdbd35c1f0e3
accelerometer: remove dead if and modernize

Based on a coverity warning.
nss-myhostname: use _cleanup_ and split function into two

The triply nested loop is just too much. Let's split out the
middle loop's body, so the whole thing is easier to read. Also
modernize the style a bit, using structure initialization to
avoid memset and such.
nspawn, machine-id-setup: warn if read-only mount call fails

They are not crucial, but they shouldn't fail.
bus: check return value from bus_type_get_alignment/size
journald: check return value of strappend
bootchart: split out option parsing from main()
bootchart: fix a potential buffer overrun

If the configured number of samples was close to MAXSAMPLES,
the samples buffer could be overrun:

- by 1, because of off-by-one in the condition (samples > arg_samples_len),
and
- by many in case of an overrun, because the number of samples to
  capture was increased, instead of being decreased.

Simplify things by converting to a normal for-loop.

In store.c: change buffer size from 4095 to 4096. 4095 is a strange
number.
strbuf: fix leak on memory error

Not very likely, but let's fix it for the matter of
principle.
strbuf: replace quick sort with bubble sort

No need to call the heavy artillery, when the original array
is sorted. Reduces complexity from n² log n to n log n, where
n is the number of items in the array, not very large, but
still.
Modernization

Use _cleanup_ and wrap lines to ~80 chars and such.