* sbr/m_getfld.c: fix two bugs which could cause us to walk off

* sbr/m_getfld.c: fix two bugs which could cause us to walk off
the beginning of the stdio or prefix-string buffer when checking
for presence of the end-of-message delimiter in some situations.
This might cause inc to dump core if you were unlucky. (This was
Debian bug 359167.)
* test/tests/inc/{md5sums,msgheader.txt,test-deb359167,
test-eom-align,fromline.txt,filler.txt,deb359167.mbox}: new tests
both for the specific problem and to try to check various alignments
of the eom string with the stdio buffer ending.
* test/common.sh: Added some functions for doing progress indicators.