Fix some issues reported by lintian

Fixes: lintian: vcs-field-not-canonical
See-also: https://lintian.debian.org/tags/vcs-field-not-canonical.html

Fixes: lintian: upstream-metadata-file-is-missing
See-also: https://lintian.debian.org/tags/upstream-metadata-file-is-missing.html


Fixes: lintian: upstream-metadata-missing-bug-tracking
See-also: https://lintian.debian.org/tags/upstream-metadata-missing-bug-tracking.html


Fixes: lintian: upstream-metadata-missing-repository
See-also: https://lintian.debian.org/tags/upstream-metadata-missing-repository.html

Fixes: lintian: uses-debhelper-compat-file
See-also: https://lintian.debian.org/tags/uses-debhelper-compat-file.html

Fixes: lintian: package-uses-old-debhelper-compat-version
See-also: https://lintian.debian.org/tags/package-uses-old-debhelper-compat-version.html

Problem: some systems can't find pcre.h

Solution: help by pre-populating a CPPFLAGS value

Signed-off-by: Jim Klimov <EvgenyKlimov@eaton.com>

Problem: no test for issue #11

Solution: add teststr.gsl to make check and add non-matching search_replace to test

See #11

Problem: memory leak if string.search_replace has nothing to replace

Solution: use mem_strdup instead of strdup

Fixes #11

Problem: Build can't always reasonable run binary

Solution: Build the test stage instead, since that's where
the ./gsl -v build was moved

Solution: Put the ./gsl -v  call in check: and make check: depend
on everything: to make it easy to see in Travis.

Problem: gcc is not always called gcc

Solution: Query the --version string of whatever CCNAME happens to
be. This will catch such misfits as cross compilers, and places
where gcc is invoked as plain old cc.

Problems: more improvements needed for debian packaging

Solution: list them under BSD-3-Clause