Add const to strings in skeletons/

This reverts commit 233be538.

Add (void) when st is unused

Missing void in _new_stack()

Fix duplicate 'const' warnings

Fix issue 144

Merge pull request #154 from brchiu/vlm_master_merge_pr99_mouse_2c8d366b_solve_prob_for_s1ap_nbap_dsrc

Merge PR99 and its fixes to support parsing Information Object and Information Object Set

Since the typedef of asn_INTEGER_specifics_t also contains a const the
compiler complained about:
"warning: duplicate ‘const’ [-Wpedantic]"

This removes the GCC warning:
"warning: function declaration isn’t a prototype [-Wstrict-prototypes]"

This is to get rid of the GCC warning:
"warning: unused variable ‘st’ [-Wunused-variable]"

This removes the GCC warning:
"warning: initialization discards ‘const’ qualifier from pointer
target type [-Wdiscarded-qualifiers]"
from BIT_STRING.c and ber_tlv_tag.c.

Travis CI failed due to weird reason :

  The log length has exceeded the limit of 4 MB \
  (this usually means that the test suite is raising \
  the same exception over and over).

  The job has been terminated

A temporary solution is removing `make check` and
only perform `make distcheck` to reduce log size.

Excerpt from commit log :

  Do not generate coverage data for the test C code
  When compiling tests remove the CODE_COVERAGE_CFLAGS flags from CFLAGS

and also add

  CFLAGS = $(filter-out $(CODE_COVERAGE_CFLAGS), @CFLAGS@)

to 'skeleton/Makefile.am' to avoid compilation error in vlm's repository.

This is a collection of works :

1. Based on @zhanglei002's pull request 99.

2. A fix by @AuthenticEshkinKot and merged by @mouse07410 at
   commit 2c8d366bbe1fc4e4c041e9b0eb9779f8a42d754b of https://github.com/mouse07410/asn1c
   to support parsing of Information Object and Information Object Set

3. A fix by @Uri Blumenthal in asn1fix_derefv.c at :
   commit ec0ade4f87c807e763e3f35fc5466adb6dda3473 of https://github.com/mouse07410/asn1c
   to solve crash on asn1p_value_free().

4. My pull request 18 to @mouse07410's https://github.com/mouse07410/asn1c to solve
   problems found during parsing ASN.1 modules of S1AP, RANAP and J2735-201603.

5. My pull request 22 to @mouse07410's https://github.com/mouse07410/asn1c to solve issue 147
   and to solve the problem during parsing ASN.1 module of NBAP.

6. My pull request 23 to @mouse07410's https://github.com/mouse07410/asn1c to fix memory leakage
   introduced in aforementioned commits.
   Most code changes are the same as pull request 153 to this repository.

7. A fix of my bug in item 6 which result asn1c crash, fixed by @mouse07410.

Skip last comma when there are no extensions