PGPRO-6601: Add prefix to global variables and functions.

[shinderuk]

This is necessary to avoid name collision with other modules. Where possible,
make variables and functions static.

Before:

% nm -gU pg_wait_sampling.so                                            
00000000000014cc T _Pg_magic_func
00000000000014f8 T __PG_init
0000000000002bec T _alloc_history
00000000000014d8 T _check_shmem
0000000000008020 S _collector_hdr
0000000000002c24 T _collector_main
0000000000008010 S _collector_mq
000000000000210c T _init_lock_tag
0000000000001d04 T _pg_finfo_pg_wait_sampling_get_current
0000000000002764 T _pg_finfo_pg_wait_sampling_get_history
0000000000002124 T _pg_finfo_pg_wait_sampling_get_profile
000000000000269c T _pg_finfo_pg_wait_sampling_reset_profile
0000000000001d10 T _pg_wait_sampling_get_current
0000000000002770 T _pg_wait_sampling_get_history
0000000000002130 T _pg_wait_sampling_get_profile
00000000000026a8 T _pg_wait_sampling_reset_profile
0000000000008018 S _proc_queryids
0000000000008038 S _queueTag
0000000000008028 S _recv_mq
0000000000008030 S _recv_mqh
0000000000002b38 T _register_wait_collector
0000000000008000 S _shmem_initialized
0000000000008008 S _toc

After:

% nm -gU pg_wait_sampling.so                                                
0000000000001560 T _Pg_magic_func
000000000000156c T __PG_init
0000000000001d74 T _pg_finfo_pg_wait_sampling_get_current
00000000000027dc T _pg_finfo_pg_wait_sampling_get_history
0000000000002194 T _pg_finfo_pg_wait_sampling_get_profile
000000000000270c T _pg_finfo_pg_wait_sampling_reset_profile
0000000000001d80 T _pg_wait_sampling_get_current
00000000000027e8 T _pg_wait_sampling_get_history
00000000000021a0 T _pg_wait_sampling_get_profile
0000000000002718 T _pg_wait_sampling_reset_profile
0000000000008010 S _pgws_collector_hdr
0000000000002c64 T _pgws_collector_main
0000000000008000 S _pgws_collector_mq
000000000000217c T _pgws_init_lock_tag
0000000000008008 S _pgws_proc_queryids
0000000000002bb0 T _pgws_register_wait_collector